I have been dealing with this issue for the last several thunderbird versions. I am currently running 115.18.0 Everytime I try to configure an existing gmail account for thunderbird via File -> New -> Existing email account I specify my Name and gmail email address, then password for the gmail account. The google authentication pop up launches " Mozilla Thunderbird wants to access you Gmail" and I click "Allow" As soon as I click "Allow" I am asked to download a file. Google gemini says this file is a sign that Oauth is not being accepted by thunderbird. What I have tried. I verified Thunderbird is set to accept cookies I have verified there are no previously stored gmail passwords (as this has never worked) I have changed my default browser from Firefox to Brave and verified the same behavior please help, Thunderbird has never been able to connect to gmail when running on this Ubtuntu install.