The only other thing I can think of is deleting the Windows microcode update file.
I did this after downgrading the bios with microcode C6 still did not work
I didn't delete it just renamed it..
I than downloadeded an older version of windows 10 (from nov 2019) disabled updates and run it via usb live boot just to test if that windows version would allow undervolting but it didn't also work.
I believe the ME was updated and that it can't be reverted to an earlier version.
I think despite downgrading the bios the ME part of it is not actually being downgraded so that's why it's still staying locked?
Because when I downgraded i do recall seeing an error about ME failing.
Before posting i did hours worth of searching all your posts
@unclewebb thanks for your advice and help.