First, disable account hub in Settings/General, then accept cookies in TB Settings/Privacy & Security, disable VPN if in use, and add the account from ⩸ - New Account - Email. Omit the password until after the account is added and enter it in the OAuth2 authentication window at first opening of the Inbox.

Thanks for that quick response. However, the problem persists. To recap, I have an existing TB email client on a Windows PC. I want to use TB on a Chromebook, with the same Gmail address.

I have installed Linux TB on the Chromebook with no apparent issues. This version has no "Account Hub" or "Account Wizard", nor option to enable/disable.

"Create a new account" on the Chromebook opens a page entitled "Set up your existing email address." Required fields are "Your Ful Name", "Email address" and "Password".

I don't know anything about a TB password but enter one anyway so I can click "continue" to the next page, where it's announced that TB has successfully found my existing Gmail server configuration. It looks OK so I click "Done", then a dialog box appears that says, "Checking password", along with some animated dancing dots.

Hours later, TB is still "checking password" until I stop the operation and start over, only to have the same result. It seems a critical factor is the password I don't have. Where does one find that? I tried typing in the one saved in the TB Password Manager on my PC but that didn't work either.

Possibly some "syncing" issue with my existing account? It can't be this difficult!

If the account hub is not shown, you appear to be using a TB version 128 or lower. For gmail, the password can be omitted during setup, and on first opening of the Inbox you should see a window asking to allow TB access to the account. At this point, enter the account password, the same one for accessing the account in webmail. For the (OAuth2) authentication to complete, cookies must be accepted in TB (not browser) Settings/Privacy & Security. Also, disable a VPN if one is used.

Update: No luck yet. Apparently V. 128 is the default install on Chromebook. Following Google's instruction, after enabling Linux environment, went to Play Store where TB was downloaded and installed (V. 128 - I have V. 142 in my downloads folder but don't know how to install it in Linux.) It's my understanding that TB will update itself to the current stable release, so my inability to install V. 142 may be a moot issue. In desecration, I uninstalled TB and tried reinstalling in "terminal"; the installation was successful, but it still reverted to V. 128, and I get the same result in setup....TB infinitely "checking password", and unable to connect. So that's where I am now. Cookies are accepted in TB and there is no VPN on the Chromebook. I'll keep working at it but at the moment I'm fresh out of options. Coming from a long history with Outlook, I chose TB for Windows years ago because of similarity, and features that help with my diminished vision. Outlook may still be an option but I really don't want to go back there!

Worth checking you have the correct settings:

incoming IMAP: imap.gmail.com, 993, SSL/TLS, OAuth2 authentication, email address

outgoing SMTP: smtp.gmail.com, 465, SSL/TLS, or 587, STARTTLS, OAuth2 authentication, email address