I'll be concerned when/if my hardware shows any sign of failing
From what I learnt when tuning DDR4 timings, the trefi type stuff is affected by temperatures, every so often the DRAM needs to refresh itself, manufacturers set defaults very conservative, the reason been that at high temperatures they have to refresh more often to prevent bit flipping. So DRAM is ultimately more reliable in cooler temperatures.
However the PS5 doesnt use DRAM, it uses VRAM instead, the characteristics might be different, also an unknown is how these type of values are configured.
The instability reported on reddit, I dont think is heat related, there is people sitting on the dash and firing up a game and before you can count to 10 its crashed to dashboard. So potentially two issues, or maybe the memory isnt an issue at all. But I personally wouldnt be comfortable running hardware at 90C.