HP Elitebook 850 G6 freezes on HP secure boot loading screen,

[Hippiman]

PC was initially in a loop where the secure boot screen would come up, it would switch to a screen saying a BIOS update needed to finish, then the PC would reset and loop from the initial secure boot loading screen.

I was able to fix that by removing the battery and CMOS and waiting. I then got into the BIOS settings and ran the BIOS update, but if I let the PC load normally it freezes, seemingly as the secure boot screen is going to end (sometimes the text becomes half faded as the freeze occurs)

I have disabled all settings related to secure boot (I think). I also rolled back the BIOS version. no change.

If I try to reinstall Windows from a USB it either freezes on the secure boot screen or instantly freezes on the first screen of the Windows installation media. Trying to system restore from network but the same sort of thing happens, it looks like it is doing stuff and then freezes with a minimized powershell window in the bottom left corner. I have left it like this because the CPU fan started ramping up to max on this screen, so not sure if it is actually doing something (doubt it).

Tried removing battery/CMOS while booting, still freezes at the HP Secure Boot screen. Removed the drive. No change. Tried an empty drive, system recognizes there's nothing on it and asks to check next boot device, then it freezes on secure boot window.

Is it the boot loader? Can't seem to get to a page to access safe mode.