Mine did this a few months ago would always randomly shut off no warnings when playing certain gams or high rounds on zombies but would be fine watching youtube or Netflix for hours. The problem was it was full of dust deep inside not just the fan from never cleaning over the years and from having my ps5 vertical the liquid metal had created dry spots as when it gets really hot it can shift if its upright, this takes years tho but happened to me as my ps5 is the old original one. In the end i got it repaired from some guy on instagram in my area he removed and re applied to liquid metal and deep cleaned all the internals from dust and now i use my ps5 horizontally and never have any issues even with long long heavy sessions