@Darkness93_yt
If you reduce the temp limit you also reduce the power draw of the card.
If a game crashes the whole system it is almost always a PSU ruining into the OPP and I saw 3090 crashing system with 1000w PSUs due to load peaks that are fare higher than the TDP.
That it does not happens with your 2080ti is one more hint that the problem is on the hardware side and not software related, there is almost nothing that could crash the entire system, without a blue screen, on the software side anyway.
So imho the PSU is still the most likely culprit here. (Or the power draw of the 3090, however you see it.) 😉
I would either cap the FPS in half or seriously under-clock the 3090 to see if the issue persist.
If not it is one more hint towards the PSU.