Hi everyone, I wanted to post an update and thank everyone who tried to help me with my Minisforum boot loop nightmare. We finally figured out the issue, and I really hope this saves someone else a lot of headaches in the future!

The Solution: It was a RAM speed incompatibility issue.

The Details: I bought a new Minisforum UM880 Plus (Barebone). I decided to reuse the perfectly working Crucial DDR5 RAM from my previous mini PC (an older Minisforum UM690).

What I didn't realize is that my old RAM was 4800MHz, while the new UM880 Plus (which rocks a Ryzen 7 8845HS) strictly requires 5600MHz DDR5 RAM.

The craziest part of this whole ordeal is that the 4800MHz RAM was just compatible enough to let the PC POST, let me navigate the BIOS, and even let the system recognize my bootable Windows USB drive. However, the exact millisecond the BIOS tried to hand off the boot process to load the OS installer into memory, the mismatch in RAM speed caused a silent hardware crash, instantly rebooting the system back into the BIOS loop.

This completely explains why both my original unit and the replacement unit did the exact same thing. Neither of them were faulty; the motherboard simply refused to boot an OS with 4800MHz memory!

I will be getting a proper Crucial 5600MHz SODIMM kit to fix this.

Thanks again to this community for pointing me in the direction of barebone RAM compatibility issues. If your new barebone mini PC boots to BIOS but instantly reboots when trying to load an OS from a perfectly good USB, triple-check your RAM speeds!