Disable SafeBIOS

Heya folks,

Got a few new Latitude 5530's that I want to downgrade from Windows 11 to Windows 10 - They're outlet machines that came with Dell SafeBIOS. 

When I first got them - If I put a USB stick in, either USB C or USB 3 ports, the machines would go in a boot cycle, and restart - even if it was waiting to go in to BIOS or Boot choice (i.e. hitting F2 or F12) 

I booted the machines up to Windows 11 to get a BIOS update, thinking this would change the behaviour, but now the machines turn off, instead of going in to a boot loop - even if you've hit F2 or F12. 

Can anyone advise where I go to disable whatever this is? I can't find anything in the BIOS itself that stands out ?