Uwe,
> looking at:
> https://packages.debian.org/search?keywords=thunderbird&searchon=names&suite=stable§ion=all
> this lists the thunderbird packages from buster, while bullseye is the
> current stable release.
> Probably related to that packages.d.o doesn't know about
> bullseye-security and bullseye-backports.
Rhonda D'Vine submitted a Merge Request for this on Aug 16:
https://salsa.debian.org/webmaster-team/packages/-/merge_requests/21
I don't know what is taking so long for it to be merged.
Daniel Lewart
Urbana, Illinois