Seeking help

So I’ve posted on other forums but really no help not sure if here is the right place but y’all are smart so let’s see.
I have 2 different ecosystems: 1.apple(MacBook Air) little info: I originally bought an m3 pro from eBay and thought i was scammed so I returned it and bought 3 different m3 airs from Best Buy not open box either. 2. Windows. I have a gaming rig I built and it has worked flawlessly until recent. Problem: First started with the gaming rig. (Windows 10 and 11) the pc would reboot and restart forcing me to reinstall the OS. this persisted for a few weeks that why I thought I’ll just buy a Mac ( I don’t game to much nowadays) but with the Mac’s listed above they all do the same thing reboot and restart forcing me to reinstall macOS. I talked to multiple apple support people and they said that it is extremely rare that this would be happening to 2 different systems. And one said it sounded like I could have a virus or malware in modem or router. So I replaced the hardware and changed passwords but with no luck the problem persists. The weird thing is I’ve taken both the Mac and the PC to my sisters and they work perfectly they never restart or reboot and work as intended. So please could someone maybe help figure out what could be causing this issue. Me and my sister are stumped and not sure what do. Thanks in advance.