Let's get something very clear - if all imap / pop gmail and outlook mail accounts have been set up correctly and OAuth tokens are in Saved Passwords, you will not be asked for any passwords when you start Thunderbird because Thunderbird uses the saved passwords and connects to the various servers automatically.

There is only one case when you get asked for a Password when starting Thunderbird and that is if you have chosen for some reason to create a 'Primary Password' in Thunderbird. If you share your computer with other people AND also allow them access to your computer User Account, you may not want prying eyes to have access to your saved passwords, so Thunderbird allows you to set up a 'primary password' and you will get asked specifically for that 'Primary Password' once per session at start up. The 'Primary Password' should be a unique password, it should never be any password you use for mail accounts. I have come across some people who had no idea what they were setting up and they used a mail account password as their Primary Password, so were confused. Clarify - on start up are you being asked for a 'Primary Password' ?

Upload an image (to this question in forum) of that initial request for password pop up so we can sort out whether you are being asked for a Primary Password or gmail account password.

In Settings > Privacy & Security scroll to 'passwords' section Is this checkbox selected 'Use a Primary Password' ?

re :But when I try to sign into thunderbird email, it asks me to sign in with my gmail account.

Assuming you still have a gmail account with google and you still have a gmail mail account set up in Thunderbird, then when you start Thunderbird, it will auto try to connect to server. You should have the imap or pop gmail account set up with an Oauth2 token password, so connection should be automatic and you should not be asked for any gmail password - unless you deliberately removed the saved gmail passwords/tokens.

Have you removed the saved passwords for gmail from Settings > Privacy & Security > Saved Passwords?

Please note - if you have set up a VPN then the gmail server will probably refuse connection and you will get a prompt to enter password.

Check computer - if you have enabled a VPN then switch it off or create a split tunneling and set up Thunderbird to use it. Some Anti-virus products offer a VPN and might have enabled it by default.

Clarify - on start up are you being asked for a 'Primary Password' ? Upload an image (to this question in forum) of that initial request for password pop up so we can sort out whether you are being asked for a Primary Password or gmail account password. In Settings > Privacy & Security scroll to 'passwords' section Is this checkbox selected 'Use a Primary Password' ?

Sue ?