iMac randomly shutting down, suspected faulty SMC

Hello, my iMac kept shutting down after a few minutes of use in windows, and I totally couldn’t boot to macOS as it shut down while it is booting. I reset the SMC , and it worked for a few hours, until it shut down again after a few hours. I think that chip might be faulty, but I have no idea how to replace it, and I’m not even sure if it’s causing the problem. I don’t want to replace the whole motherboard though. Please link to some guides on how to do it, or should I just have it repaired, but by who? It’s warranty has expired quite a while ago.

I did an aida64 stress test in windows, the fans were ramping up like normal, and cpu temps were at around 99 which is normal for a mac. No shutdowns. I used HWmonitor to measure the temps. Idle temperatures were at around 50 to 60.

I managed to boot to windows and macOS consistently after resetting the smc, and also got to playing some games. However, trying to launch Yakuza 0 seemed to immediately turn it off. I also got to playing an indie game called Noita, and it seemed to only shut down when the game was closed. It’s not the most graphically demanding game though, and I haven’t tried anything on macOS yet.

Tried doing diagnostics, no errors. Seems to turn off when opening programs, closing programs, taking screenshots etc. Can’t be sure that those are the only times that it turns off.