Its been a while since I tried but installing Debian Bullseye for the Pi from debian.org is pretty easy.
To add a GUI, you need to run tasksel (which may need to be installed with apt first)
Preempt_RT would not install from the repos so I had to use this method mentioned earlier
github.com/kdoren/linux/releases
QTPYVCP and PYVCP is a problem because they need VTK which is not available from the pi repos. It is possible to build it but its an overnight job.
ftree built a image which is discussed somewhere on this forum but his code is here and includes a VTK whl:
github.com/kdoren/linux/releases
Note this is crosscompiled on a AMD64 linux box. I did it on a virtual instance on Windows.
I did finally get QT running!
