https://onelaboratories.us/rtai_lcnc/ 
copy each and install using: 

sudo dpkg -i (place the deb file here)

10:45 PM lcnc-relay: <captainhindsight_.> reboot and choose the RTAI kernel

starting from a Debian 12 install without linuxcnc-uspace installed
IF linuxcnc-uspace is already installed then you need to run sudo apt purge linuxcnc*

Grub Customizer set: quiet isolcpus=1 (2,3) idle=poll
sudo update-grub

<captainhindsight_.> this ^^ is what worked every time today
<captainhindsight_.> this assumes that you are already in the directory with the debs in your console
 RTAI latency on i5's and core 2 duo's is <4uS until you load firefox and even worse when you play a video