Check the version of git on typing git -- version in terminal . once got git version then

Check if you're in a Detached HEAD state

Go to View > Git Repository.

If it says HEAD instead of a branch name, you are in a detached HEAD.

check if the branch was deleted or renamed remotely

Go to Git > Manage Branches in Visual Studio.

See if any branch is listed under Remotes/origin/.

If you see only main and not master, then maybe master was renamed to main on GitHub