I did bad asking.
I did update to Debian 11.
The update was successfull.
Then after update system was asking:
Now I can only boot the recovery modus.
There are several things that could cause a kernel panic. The first place to look is the logs.
If you can boot up with an older kernel that works, which you may be able to choose from the grub menu, if it appears, then you could look at the logs in /var/log, in particular the files syslog or syslog.1 and kern.log. To get the systemd log run something like:
where -b1 means the boot before last, which I'm presuming is the kernel panic boot, and find the log entries at the time of the panic. The -b has to be adjusted to get the right boot ... see the man page.
Looking towards the end of the logs just before the panic is where some useful info is likely to be.
This command may give info on errors, but there may not be much about the kernel panic itself:
Kernel panics may not leave lot of info in logs because once they panic they stop outputting, but just a few hints may be helpful.