Thanks. v6.1 is available on bullseye-backports. I installed it and
the trouble is gone now.
BTW, does non-free firmware tied to kernel version?
I use firmware-realtek to deal with my dragon 2.5G NIC that seems to
be unstable without realtek-firmware. I want to make sure I use the
correct version (for linux v6.1), if there is such a requirement.