Ok, update on the update issues:
I could not migrate VMs from the older backup server which was upgraded to 8.3 RC1 back to 8.2 install, so I'm forced with having to continue troubleshooting it.
Today I tried to start a CD install from efi shell and I finally got an error / output as to why install fails silently:

"This build of Xen requires NX support"

I guess I had it disabled in the BIOS, just wish the install would have output the error with a wait prompt or something, rather than a silent failure.

Edit: Confirmed; after enabling execution disable option within bios, installer booted without issues and the install is currently ongoing.

@yann Good catch. I tend to use net install when available, as it is faster than emulated iso on supermicro motherboards. When trying beta 2 install, I did use the network source by using xcp-ng-8.3.0-beta2-netinstall.iso.
To test things further, I used my backup server (Supermicro X10DRT-H, with E5-2630 V3) and disabled execute disable bit. Verified that 8.3 RC1 install gives the same error "Xen requires NX support" and ran beta 2 install from local media. This time 8.3 beta 2 was installed without issues and after a reboot I verified that execute was still disabled in the bios.

When using RC1 installer:

Beta 2 installer with local media this time:

Forgot to mention that I did try installing RC1 via legacy bios onto the system (installer would work in that case), but I could not get the system to recognize boot disk (NVME) after the install (installer itself saw and could use said disk).
Ended up discovering issue with EFI installer prior to fixing the legacy path as I've not spent much time on that since legacy bios would not be supported down the road.

@yann Never got that far, 8.3 beta 2 would not boot after the install.
Difference with RC1 is that the beta 2 installer itself did not check, or could re-enable NX support, but the actual boot of beta 2 would fail similar to RC1 installer (likely due to NX support being disabled).
So I could install, but not boot, the beta 2 onto the system. My previous posts don't provide much detail, but here is how it went: https://xcp-ng.org/forum/post/80208

@andyhhp thanks, seems issue was most visible within RC1 install. 8.2 worked well with NX disabled (I guess by activating it on it's own), beta 2 would install, but not boot (have not tried beta 1), and RC1 would fail seemingly silently.

The efi path is not to activate the NX setting, it was just me getting to the cd directory with the bootx64.efi launcher for the installer. Running it this way, rather than allowing BIOS to boot into CD directly is what allowed me to see the output of the installer prior to exit: "This build of Xen requires NX support". Normally the next boot option would take over and this text would not be seen.

My setup is Supermicro X10SRM-TF motherboard with E5-2699 V4 processor, latest bios, UEFI boot.
I don't even remember when I disabled NX support, perhaps couple of years ago when playing around with increasing single core performance.

@olivierlambert Thank you. Install went smoothly and I'm in the process of transferring all of the VMs from the backup server back onto my main workhorse.

I just wish I remembered an old troubleshooting tip:
When something odd is going on, reset the bios to defaults (or something along those lines).

I did figure out a way to run the installer from efi shell; never done that before. Wish I thought of it sooner as well (no telling how many times I've rebooted this system trying to troubleshoot things.

Ok, update on the update issues:
I could not migrate VMs from the older backup server which was upgraded to 8.3 RC1 back to 8.2 install, so I'm forced with having to continue troubleshooting it.
Today I tried to start a CD install from efi shell and I finally got an error / output as to why install fails silently:

"This build of Xen requires NX support"

I guess I had it disabled in the BIOS, just wish the install would have output the error with a wait prompt or something, rather than a silent failure.

Edit: Confirmed; after enabling execution disable option within bios, installer booted without issues and the install is currently ongoing.

I've tried to do a "clean" beta 2 install, same issue (efi shell).
I've changed bios to legacy boot and was able to run a RC1 installer (nice bootup graphic and all), but it warns you that such method will not be supported:

So I ended up using said installer to recover 8.2 install from backup and I'm back up and running at 8.2 (via EFI). Not sure what part of my config could cause issues with 8.3.

Decided to try updating to beta 2 and... install went smooth, but system now refuses to boot.
Seems issue is similar to RC1 install. Boot fails silently, similar to install on RC1, and next boot option is executed. But while the RC1 failed into a working 8.2 install, 8.3 boot fails into EFI shell.

@yann, No seems Beta 2 works as it should. Though I'm hesitant to go that route since RC1 is available. Is update from Beta 2 to RC1 save / reliable to do via internal updates without ISO?

I'm having issues updating via ISO on supermicro motherboard. I have a netinstall iso mounted (though I've also tried a full ISO via usb), and can get to the initial "install" bootup prompt from 8.3 RC1 image.
Issue is that once "install" option is chosen, "Booting install" shows for about a minute, screen blanks and normal bootup occurs instead. No sign that booting the install has ever occurred.
Do I need to wipe the SSD with the 8.2 and just do a clean 8.3 install? Is there anything I can do to get a more detailed view of logs / or what else could have gone wrong?
If this has been covered, I apologize, I tried reading through 500+ messages in this tread, but nothing stood out to me describing a similar issue.
Supermicro X10SRM-TF motherboard with E5-2699 V4 processor, latest bios, UEFI boot.

If I choose install, or let it run automatically, same results.

This is shown for about a minute

Than ready to boot prompt flashes for a sec.

And it goes to a normal xcp-ng bootup...