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.

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.