Just go a Linux download page - Ubuntu is easy to use. Download the image, burn the iso to a USB and just boot from that. Select the 'live' option. It won't install anything unless you select 'install' once fully booted, but you can still use the OS. Nothing to be afraid of and if you are going to be installing Windows again anyway, even if you do proper install, you can just remove any partitions when you reinstall Windows again. I don't know if you might be able to find out anything useful of not, but even knowing if Linux will boot probably eliminates CPU problems.
If Linux won't boot either, then I would think that you do have a CPU, memory or maybe GPU problem. It might just help to start eliminating possible causes for your problems. Have you tried removing the GPU and using just the internal graphics? I think it's going to be a case of eliminating one thing at a time until you find the culprit.
Forgot to say, since Linux is not a Microsoft 'approved' OS, you might need to turn off Secure Boot and allow 'Other OS' in your UEFI/BIOS options for it to work.
One last suggestion, forgetting Linux for a moment, might be worth flashing the latest BIOS. Looks like 0703 is correct for your board. I don't have a Z790 so I don't know the BIOS history myself, but as far as I know that version is stable and it might have some microcode that gives better stability while you install Windows. Perhaps somebody else here can suggest what BIOS they have found to be good. In your case, you will have to update the BIOS before ME. That could cause a temporary problem seeing one of the M.2 slots, so you might need find one that works. Hopefully that won't be the case. Once you have Windows working, you can update ME afterwards and all will be well.
Z690 Hero, 12900K, BIOS 3701, MEI 2407.6.1.0, ME Firmware 16.1.32.2473, 7000X Case, RM1000x PSU, ASUS TUF OC 3090TI, 2 x 16GB Corsair RAM @ 5200MHz, Windows 11 Pro 23H2, Corsair H150i Elite AIO, 4x Corsair RGB fans, 3x M.2 NVME drives, 2x SATA SSDs, 2x SATA HDs.