Installation Nightmare! All out of ideas! :-(

No offence taken Robert, I find that starting any engineering discussion with 'Explain it to me as if I know nothing' is often a very good place to start! .
Now that I have linux installed (on both devices) I should probably start a new thread in the Probe Basic section?

I did briefly try the Pi 4B with the 64 but bullseye version of Pi OS. I found a preempt_patch which installed ok, QT5 installed OK. But VTK did not run. I also could not install ethercat which I think was related to the RPi kernel not being in step with a normal Bullseye version 5.10.

So being unable to run QTPlasmac or Ethercat, I gave up as it was of no use to me.

But aside from all that, the latency was remarkably good, similar to a J1900 or I3. If you were just using gmocappy or axis, it is worth considering..

I'm a BIG fan of the little Pi's, we use them for all kinds of amazing stuff like multi million dollar data systems in mining where a Raspberry Pi is the ONLY interface between the production PLCs and the production reporting! . I also use one for switching guitar patches on the Fractal Axe processor in my band!
BTW, I just posted some info on my build in the 'Show your stuff' section.
Thanks again for the help.

Sorry, one more thing, is there some secret to getting wifi working in this Debianedu12? When I open a terminal and it doesn't understand the command 'ifconfig' my heart sinks!

I think ifconfig needs to be installed: sudo apt install net-tools
technically its depreciated. 
ip a gives a lot of info try it first.
 

Everything is so different in the distribution, I feel like I'm starting again!
I don't see any wifi interface listed using ip -a. I know it has one as it was working when Windows was still installed!