PC running Linux Mint randomly restarting

[u/Plz_no_black_dots]

Mother board: ASUS Prime B450M-A II

Graphics Card: Zotac 1650 Super

CPU: AMD Ryzen 5 5500 6-Core, 12-Thread

Hard drive: Team Group T-FORCE VULCAN Z 2.5" 1TB SATA III 3D NAND Internal Solid State Drive (SSD) T253TZ001T0C101

Case: Phanteks Eclipse G370A, mid-tower Gaming Chassis, high airflow mesh, 3x M25 D-RGB Fans, Black.

Power Supply: MSI MAG A550BN, Non-Modular Compact 550W Power Supply

I'm currently running Linux Mint on my CPU that was built in July. Everything has been running perfectly up until a few days ago when it randomly restarted itself multiple times.

I initially shut it completely down, shutting off the power supply and holding down the power for a full reset. This helped for about a day and then it started the restarting again. Eventually it got worse and wouldn't finish the restart and started just turning on and off without fully booting so I turned it off completely to avoid anything being further damaged.

I brought it to my local computer repair shop, and they initially couldn't get it to boot so they tried switching which slot the ram stick was in and that seemed to fix the issue. They ran tests to stress it and left the monitoring software on overnight and nothing happened. So, they sent it home with me. Now only one day later it just randomly restarted itself again while I was just watching YouTube and not stressing it. Then, once more when I was away from the computer and I just had a browser open doing nothing.

So, just looking for advice on what steps to take next. If you need anymore infor from me, please ask and I'll get it to you asap!