I would add that many modern computers are almost hardwired for
Windows. ...
So I gave up, and just installed bookworm clean. No bootable OS found.
I'll cut it short: it wouldn't boot because a /boot/efi/EFI directory
did not contain a Microsoft directory containing bootmgfw.efi.
Previously, it had been happy to boot from the Linux EFI file, but
obviously only because this wretched Windows setup was there. Just to
be on the safe side, I copied shim64.efi and renamed it bootmgfw.efi,
all in a directory named Microsoft. No problem now.