New and Working RTAI debs for 2.9

Hi everyone, total noob here. I'm experinenting the linuxcnc. I have an asrock j3355b board. I'm planning to use it with parallel port. I tried to install debian and linux cnc 2.9.2 but I cannot solve the kernel issue. When I install debian 12 it comes with kernel 6.x.x and all the RTAI kernel and other stuff is for kernel 5.4. as I understand that kernel and RTAI packages needs to be same. How do you install debian 12 RTAI, please help or direct me to correct direction.

I assume that this procedure does not work when starting with a clean version of LMDE6? I tried on several systems, but I get long lists with missing python modules and the grub menu does not work.

Regards, Rob

After installation of the 5.4.279 rtai kernel + the matching Lcnc version  and a reboot, applying rt_setup and rebooting again,
starting a the axis demo for the first time often causes the system to hang or the run to abort with errors.
This happened with about 7 tries on two different systems (a 4 core Intel - isolcpu=3 and a 6 core AMD - isolcpu=2,3,5).
Info attached, as well as a run of the RTAI testsuite (odt file).
The second start of the axis demo gives an RTAI warning, but ignoring that the demo works perfectly to the end.

Running the latency test for the first time usually shows permanent 0's for both fast clock and servo.
Starting the second time it works, but the servo thread is always 999725 at start, but clearing that both values stay below 10000 with multiple gears and browsing.

Edit: Any suggestions what is wrong here?
Thanks.

Robert