I have a Gandi account which connects fine.
On the same computer, another user account accesses my gmail account with
IMAP fine through Thunderbird.
For a new user, also want to access to my gmail account with IMAP.
Are you suggesting that there's some conflict with the server config,
where Thunderbird is trying to apply Gandi settings for Gmail?
I just loop through the web login through Thunderbird, followed by
branting access on my phone, then start over.