Windows Mail keeps saying my gmail account needs attention

Also look in Windows Settings > Accounts > Email & accounts. If an old copy of the Gmail account is sitting in there, Mail keeps picking it up again and you get the same warning even after you re-add it. Remove it from there as well, then add it back once.

did you change your google password or turn on 2-step recently? that's usually it. remove the account from Mail completely and add it back, and pick the Google option rather than Other account so it does the proper google sign-in. if you're on the old Mail and Calendar app though, Microsoft retired that one, so it may never stay fixed. the new Outlook app is where they want you.