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How to convert UTC time on server side to be users local time on a GET request?

I am trying to check if the date of the last time an element was clicked is equal to the current date. The current date is being created by the server and is 5 hours ahead of my local time, so at a certain time of day, the code stops working correctly because the program thinks it's now the next day.
Here is the code that is causing issues on my server side:
let todaysDate = new Date().toString().split(' ').splice(0, 4).join(' ')
let todaysDateMs = new Date(todaysDate + ', 00:00:00').getTime()
Promise.all([
Habits.updateMany({}, {
$set: {
todaysDate,
todaysDateMs
}
}),
Habits.updateMany({ lastClicked: { $ne: todaysDate } }, {
$set: {
clicked: 'false'
}
}),
The date that is being stored inside todaysDate is in UTC time and is 5 hours ahead. When it compares lastClicked (which is sent along with a PUT request from the client side in their local time) to todaysDate, it is setting clicked to false incorrectly because of the discrepancy between the timezones.
I am wondering if I can tell the server to create a date in the users local time or any way that I can work around this issue so that the two dates are the same. I don't want specific timestamps included, only the day, month and year.

Have you tried something like Moment.js? It makes dealing with things like this a lot easier. Check out their documentation or tutorals like this.

Generally, times on servers are done in UTC and only at the client is it converted to/from their time zone. This removes the need for the server to know anything about the client's time zone.
The client will need to send their time zone along with the lastClicked time. Then your server can read this time and adjust for time zone automatically. One example is to send the time in ISO 8601 format 2023-02-07T18:25:19-05:00 where the -05:00 indicates that this time is 5 hours behind UTC.
Alternatively, the client can pre-convert the timestamp their sending to UTC. JavaScript provides ways to do this, as do libraries such as Luxon.

Date values in MongoDB are stored as UTC time - always and only. You should never store date/time values as string, it's a design flaw.
I your case I suggest a 3rd party library like moment.js, Luxon or Day.js
They provide functions like DateTime.now().setZone('America/New_York').startOf('day').toJSDate();
With these functions it should be fairly easy to solve your requirements.

How to convert a date object representing a point in time to a date object representing a day with zeroed time parts in moment.js

I need to represent date in the format 2021-11-21T00:00:00+00:00 but I get 2021-11-21T00:00:00+05:30. Please help me with this
moment('2021-11-21').format(); //2021-11-21T00:00:00+05:30

I had a similar problem when dealing with dates and birthdays in Golang, but this also applies to Javascript, I'd say. You should not try to use a date object for this task, because you can never fully rely on that when a clients browser is set to a different time zone. I ended up creating a date object myself, consisting only of 3 integers for day, month, year. By doing so you can be sure that time does not play a role at all.
By the way, this might be of interest to others as well: I did some research on how birth dates are handled in general, because when you think about it, your birthday is actually a point in time, so your birthday could change to the previous or the following day, if you look at it from a local perspective. I found out that birthdates (or dates "in general") are not considered as a time or datetime, only the year, month and day are important and they are always the same, regardless of the place/timezone you were born and regardless of the timezone the client lives in.

Instead of using moment, you can use moment-timezone and set it to GMT-0.
var moment = require("moment-timezone");
const time = moment().tz("Etc/GMT").format();
console.log(time);
And the result is something like:
2021-10-26T11:39:15Z
So I think you can't do that (except manually remove the 'Z' and add the +00:00) part as an extra string.

All dates are represented in your system local timezone. This means that moment('2021-11-21') is midnight of November 21st in your timezone (2021-11-21T00:00:00+05:30). If I run the exact same method then it will be local for my timezone (2021-11-21T00:00:00-06:00). If you need this to be in a specific timezone, or in GMT, then you probably want to use moment-timezone and cast the date to that timezone.

moment('2021-11-21').startOf('day').format()

The date 2019-04-01T00:00:00.000Z gives me previous month (March, not April)

So, I have the 1st day of month as 2019-04-01T00:00:00.000Z
When I use moment(date).month(), it returns me 2, not 3.
So, I receive March, not April.
What is the problem with it, and why I receive the previous month from the date? Maybe the problem in the TimeZone? Because my TimeZone is GMT-4, so, maybe this is problem?
Should I use UTC or ISO string instead to work with the date?

Like you mentioned, your timezone is GMT-4. The date that you are providing is in UTC. The 'Z' at the end stands for Zulu time, which is the same as UTC.
momentjs will convert this to local time.
How to handle this all depends on what you need the date for.
If this is a date that you saved somewhere before on a server, it might be important to add the correct timezone to it when you are saving it.
Be careful if you let a server create these dates, because the server might be running in a different timezone than your client.
If you create a new Date() in JS it will return a date object with the current time of your local time. If this happens on a server that's running in a different timezone, or in UTC (for example Docker containers), it will create a date in that timezone.
The best way to solve this is to think about your exact use case.
There are tons of articles written about handling dates and it's not easy.
If you have some time, this podcast helps to explain how dates work and will help you to get a better understanding of dates in general:
Coding Blocks - Why Date-ing Is Hard

Convert set date to user's local time automatically

I am creating an application where I have a pretty big set of dates and times, and I need to display these in the user's local time and date. All set dates and times are in BST; so for example 08-24-2014 16:00 BST = 08-24-2014 11:00 EST. Now, before coming here I spent good 3-4 hours looking for an answer but if anything, I got more confused. Is there any way, to convert a set of BST dates and times to the user's local settings automatically without them setting the time zone etc?
p.s.: I have two ideas in mind but I don't know if they would work nor how to execute them.
1) Get and change the BST date and time and convert it to a unit of measurement; get and change the user's local date and time and covert it to the same unit of measurement as above, calculate the difference in the new measurement, and convert that to the user's local time.
2) Use GeoLocation to find the user's date and time/ time zone and; convert the BST to whatever the GeoLocation spits out.

you can get the users machine timezone in javascript:
var currentDate = new Date();
var currentTimeZoneOffsetInHours = currentDate.getTimezoneOffset() / 60;
see documentation here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getTimezoneOffset
having the offset you can add it to your values

there is a javascript library Moment.js which allows you to query daylight saving values for specific dates and timezones.
because all your dates are in british summer time. first query if a date is in british winter time with isDSTShifted(). and subtract() an hour.
convert the date to another timezone

Is there a simple time to get a timezone from a given time?

I need to get a timezone from a time, date is not important, but daylight savings is.
something like:
timezone = function("15:00");
Is there a simple way to do this?

I dont think you can get the timezone from the time but you might get some help from Date.prototype.getTimezoneOffset()
The getTimezoneOffset() method returns the time-zone offset from UTC,
in minutes, for the current locale.
Example:
var x = new Date();
var currentTimeZoneOffsetInHours = x.getTimezoneOffset() / 60;

No, of course not. Think about it, you're passing 15:00 to that function, presumable denoting it's 3PM. But in what timezone is it 3 PM? No way of knowing. It's like me saying it's quarter to, without saying what hour it's quarter to to.
The only way you can get a timezone in JS is by using the Date object, but that just shows the timezone of the machine on which your code is running, nothing about the TZ that "created" the time you're processing.
Also note that daylight saving isn't a global phenomenon, quite the contrary. AFAIKT, there isn't a single time-zone where DST has always been in place...

In order to get TimeZone information you need more than a Date (and an offset). You need a location.
Javascript does not know the location that it resides in but it does know the current offset from UTC. That is different than a Time Zone. The daylight savings time issue play havoc with this key difference.
This has posed problems when dealing with server applications that know their timezone and report dates as being in a specific Time Zone.
My rule of thumb has been fairly simple in this regard.
Always use Long or long (a 64 bit number) to store, pass and process dates times or intervals, only convert to Date, Calendar or DateTime objects when interacting with people.

Once you have a date object, such as with new Date(), you can use .getTimezoneOffset() to get the number of minutes between the date's object and UTC, which is timezone information you can use.