I ran into exactly the same issue as described above when updating the Thunderbird snap from revision 281 (102.6.0-2) to revision 288 (102.7.0-1) and came across this report when trying to troubleshoot. I can confirm that when using the build linked in the comment above, the Oauth2 authentication works correctly.
I ran into exactly the same issue as described above when updating the Thunderbird snap from revision 281 (102.6.0-2) to revision 288 (102.7.0-1) and came across this report when trying to troubleshoot. I can confirm that when using the build linked in the comment above, the Oauth2 authentication works correctly.