PC Rapidly turns on and off.

A little over a year ago I made my first custom pc build.
My build was successful and it worked like a charm for a while.

After about 6 months I experienced weird issues with my pc. Out of nowhere, under normal workloads and temperatures, that are no higher than 60 degrees for both the CPU and GPU, the pc started randomly fully turning off. No blue screen, no error, nothing, straight powered off. It would then power itself back on at random intervals and usually turn back on again a few times before it started working again. This kept happening over the span of a few weeks till the crashes became more frequent, and eventually, wouldn't turn on anymore at all.

I drew the conclusion that it was the PSU because the crashes were without warning.
This conclusion was verified when I used my friend's PSU to test my pc, and it started working again. I sent my PSU back and got the same one in return because of my warranty. I installed it, until recently when it started giving me similar issues, which seem to be getting worse like 6 months ago. The entire PC shuts down, sometimes turning back on and of rapidly for a few times, and sometimes taking a while to turn back on. It powers back on automatically.

Can anyone please help me? I really doubt my PSU has broken down again.
But at this point, I don't know anymore.

Thanks for reading.

• PC PARTS:
• Case: Lian Li Lancool II Mesh ATX Mid Tower Case
• Motherboard: Asus ROG STRIX B550-F GAMING ATX AM4 Motherboard
  
• Memory: Corsair Vengeance RGB Pro 16 GB (2 x 8 GB) DDR4-3200 CL16 Memory
• CPU Cooler: NZXT Kraken X73 73.11 CFM Liquid CPU Cooler
• Power Supply: Corsair RM750x 750 W 80+ Gold Certified Fully-Modular ATX Power Supply
• GPU: Gigabyte GeForce RTX 3070 Ti Gaming OC 8GB
• CPU: AMD Ryzen 7 3700x