EUI-64

Those are mandatory on every enabled interface for local link communication, like neighbor discovery and Next Hop routing protocols.

Then there is modified EUI-64.

An interface takes its 48-bit MAC address, splits it into two halves of 24 bits, inserts hex FFFE in the middle, and flips the seventh bit, which is the universal local bit.

Count from the left of the first octet.

That universal local bit has value hexadecimal 02.

Flip its value.

And remember, modified EUI-64 isn't the only interface identifier method.

For host checks, Windows provides IP config.