Does Windows 10 support UTC as BIOS time?

Yep, I had success. Don't forget disabling the "internet update" for the time!

I used the way described in the ArchWiki using a QWORD on a 64bit Win10. The NTP is done on Arch and not on Windows, but the latter isnt getting booted so often anyway.

Here's the .reg file:

RealTimeIsUniversal.reg

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation]
     "RealTimeIsUniversal"=hex(b):01,00,00,00,00,00,00,00

From ArchWiki: UTC in Windows

Using regedit, add a DWORD value with hexadecimal value 1 to the registry:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation\RealTimeIsUniversal

Alternatively, create a *.reg file (on the desktop) with the following content and double-click it to import it into registry:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation]
 "RealTimeIsUniversal"=dword:00000001

If the above appears to have no affect, and a 64-bit variant of Windows is being used, using a QWORD value instead of a DWORD value may resolve the issue.