Hi,
meanwhile I found a "solution" based on this post.
I did an
apt-cache policy unipi-kernel-modules
which revealed the available version names.
Followed by
apt install unipi-kernel-modules=1.106.1.20220308~buster-1
it installed the previous version and all is smooth again.
Still, this is a workaround but not a solution.
/KNEBB