Not sure what you are asking about....
BUT....if you are in the tax account you used last year, you probably have to start an entirely new Online account to file your 2020 taxes. Each spouse needs to start up in a new Online account with their own UserID/Password, and actually file a "Single" for 2020 (or Head-of-household if one of you has a dependent you are supporting). ((( Or unless one of you divorced AND remarried during 2020. That person could still file MFJ, but still needs to start a new tax account )))
If your W-2 at work is set up as MFJ...that is immaterial to how you file your taxes...that W-2 / W-4 setting is only there to determine how much withholding is done during the year. Yes, you likely need to file a new W-4 with your employer to make sure your withholding is set properly.
It is very difficult to remove the "former" spouse from a former MFJ tax account...thus you create a new account for yourself. And before you exit that former MFJ tax account, you need to download the PDF file fore every tax year in that account and keep in a tax folder for future reference. At some time in the future, you may lose access to that old account, and you need to keep your own copy of those files for future reference should any problems crop up.