Hi!
Okay, first of all: dissasemble the PS5 completely and remove all dust. Replace the liquid metal. Then try again.
If it's still failing, then test the power supply. It should have 12V on there all the time, even in standby mode. If this is not the case, replace the power supply and test again!
Guide for replacing liquid metal: [guide|170479|How to Apply Liquid Metal in a PlayStation 5 - iFixit Repair Guide|new_window=true]
Guide for replacing the power supply: [guide|141729|PlayStation 5 Power Supply Replacement - iFixit Repair Guide|new_window=true]
Please let us know how it goes!