On a whim I decided to do what I expected to be a quick upgrade to 24H2 on this PC -- I've had a test copy of 24H2 installed since around May, and it hasn't shown any show stopping problems. The upgrade install went normally until the 24H2 setup routine restarted the PC, and then it wouldn't boot or start to finish the installation. What worked was to turn off secure boot in the BIOS and use an Insider Preview channel ISO instead of the one Microsoft's posted on their download page -- that one would not work with secure boot on or off. Afterward I turned secure boot back on and everything seems fine. I wanted to give folks a heads up in case anyone else experienced anything similar.
This PC is Win11 compliant. The boot loader is on an NVMe drive on an X470 motherboard running a Ryzen 5700G CPU, which *might* cause or be part of the problem, and the BIOS firmware was recently updated, so the problem *might* be with the BIOS as well. It's too soon to know if this is going to be a widespread problem, or if it's limited to the BIOS firmware I'm using &/or booting from an NVMe drive on what's today an older motherboard. Microsoft has been changing the Windows boot loader to make it more resistant to Black Lotus malware & similar, and has published that they've found not all BIOS are compatible with the new setup. Worse case, an awful lot of PCs are not going to be able to upgrade to a new Win11 version -- best case is I'm the only one -- 2nd best case is Microsoft fixes Windows setup.
It's kinda funny in a way since I've not had ANY problems upgrading to 24H2 on hardware that doesn't meet Win11's requirements.