3600mhz 32gb memory kit
New build with X570 Motherboard
CPU is cooled by a 360mm AIO
1000 watt PSU
will reboot under stress test with CPU-Z hits max temp of 75c
Nothing overclocked runs stable until all core load.
Games usually cause a full load on the GPU, less on the CPU... If you do not have any problems while playing games, but still restarts when you put a full load on the processor... It is best to look for the problem on the motherboard.
A system can show a similar tendency when one of the motherboard's sensors encounters a high temperature. And this is the reason to look for the problem in the motherboard... Also your CPU 12V value seems normal. This makes it difficult to find problems with the PSU.
If you can return the motherboard, it might be better to switch to a different brand. Goodluck...