Windows not booting boot runner or boot champ

previously I used Boot Champ - but then I got a ‘Bless Failed’ error and because the software is no longer supported I thought I’d jump to Boot Runner.
It sees the windows volume OK and I can select it from the boot runner screen, but after the system restarts it just loads up macOS again and I’m back at the boot runner screen. I see a few other folks have had this issue - but I don’t see a definitive answer?
something I noticed is that my windows boot volume is almost totally full - only 290 mb free I think.

Yes, I’m having the same problem, but there is plenty of room on my Win 10 drive.

That issue is usually because there is an issue with the boot style that Boot Runner is choosing (legacy versus EFI). You can force it using a configuration profile. See here:

https://twocanoes.com/knowledge-base/boot-runner-3-setup-guide/

See:

  1. Force boot type – Normally, Boot Runner 3 will detect the style of booting for selected volumes. However, if you want to override this settings, set a specify boot type.

tim