restart during gaming

April of 2020 I built a relatively solid PC and it booted and ran fine for months until it randomly started restarting during some games. Games like, CSGO, Valorant, Minecraft have never restarted on me but then games such as EFT, The Witcher 3, Assassin's Creed Odyssey/Origins and the vast...

Got a new PC but have been getting seemingly random restarts (only) during gaming. The crashes happen at completely different intervals, can be after 40 minutes, usually is after 4-5 hours, the last crash happened after 3 days without problems. This makes it very hard(time consuming) to test...