Ryzen 7 5700G APU - Freezing and/or BSOD

Hi guys, new here.

I come in search of desperate help. Just built my PC a month ago, and can't seem to get it right. There's definitively something wrong and I don't know what else to do.

It will randomly freeze, sound keeps going, and after some seconds screen goes black, and complete lockup. Will do it every couple of hours at least.
Sometimes it will go BSOD too, or tabs in Firefox crash randomly. Very, very unstable.
The lockups happen especially when gaming or doing 3D rendering stuff.
I have tried with W11 and W10 with no noticeable difference.