[AnotherGoodName]

FWIW EFI bioses absolutely can support Bluetooth which is unsurprising since EFI is a full fledged OS in its own right.

You still need to check if your motherboard supports Bluetooth at boot but many do.

[AshamedCaptain]

I have not found any outside Apple's. Do you know some models?

[h4ch1]

My mxkeys works flawlessly during the grub menu on both a MSI and a HP laptop I have.

[AshamedCaptain]

This cannot be true. How is the pairing done? Are you sure you're not using Logitech's own receiver?