There have been a few reports about the ROG Maximus Z690 Hero catching fire, and the root cause of the issue seems to stem from an incorrectly installed motherboard capacitor.

Buildzoid found that the burnt-up metal-oxide-semiconductor field-effect transistors (MOSFETs) in the faulty boards all exhibited one thing in common. The capacitor was inverted which was likely causing polarity reversal and capacitor failure as a result of malfunctioning.

The boards with the blown-up capacitor seem to have the capacitor placed in reverse

A person whose faulty motherboard didn't catch a tiny fire or something, then you could also be facing another problem. The DDR5 DRAM you installed could fail to be detected on such a board, giving off the error QCODE 53, which is a memory detection failure error.

This is happening because the burnt MOSFETs are cutting off the 5V supply that goes to the memory's voltage regulator module (VRM), causing it to shut down.