After this command update-initramfs -k all -u
all works fine for all installed kernels (6.4.0-4-amd64, .6.1.0-0.deb11.11-amd64, 6.1.0-0.deb11.9-amd64).
So I could confirm that this issue was probably caused by the udev 252.5-2~bpo11+1 package or another systemd function that hangs with my old rules that I mentioned earlier.
-- Rpnpif
