Source: thunderbird Followup-For: Bug #1028885 This looks like a similar/identical problem in the 'mozbuild' Python scripts under Python 3.11 as experienced in Debian bug #1028716 for the mozjs102 package.
The contents of the (quilt) patch used to fix #1028716 can be cherry-picked (with one conflict to resolve in the 'debian/patches/series' file) and do apply cleanly using quilt against the thunderbird '1:102.6.0-1' tag using: git cherry-pick -x f51a1f902757c4f10f7c75dfa541fb673ecab6c2 (I haven't confirmed whether the build succeeds with those changes in place, though)
