I didn't notice the download default was Windows 11 25H2 and not 24H2
I had done so many of these that I didn't even think about it.
I assume I could have changed the option to 24H2
You can't jump from Windows 10 to 11 25H2. At least mine wouldn't boot.
The BIOS was set to Legacy and the disk was MBR.
This may have been the problem.
It's hard to believe that none of the 14 previous PC updates I did were not Legacy, but it is possible.
All of them were updated to 11 24H2 and then 25H2 later. 25H2 did not exist when I updated.
Going forward I will make sure to change the OS disk to GPT (another story).
And change the BIOS to UEFI before updating to Windows 11.