Have the same issue with my system:
HP Elitedesk 800 G4 SFF with Intel i5, 16GB RAM, 256GB M.2 SSD, 4TB HDD.
Changed RAM already and tried different Kernels but getting reboots several times a day. Very annoying. Logs dont show anything helpful.
Searching the internet, many people seem to have this issue which nobody has a solution yet...
I have an Elitedesk 800 mini.
Have you by any chance have TPM enabled in the BIOS? I disabled TPM alltogether and since then no more reboots/freezes.
(running pve 7.4 and kernel 6.2.11)