In my previous post,
I wrote something like
"You can't operate wireless new XTR and similar with 12-speed road STI levers"
but I received a comment saying that was incorrect — if you pair the rear derailleur and STI lever,
you can operate it.
I apologize for my error. Thank you for the comment.

The difference between wireless new XTR, new GRX, and similar
and 12-speed road component rear derailleurs is
whether the battery is built into the seatpost and hardwired, or
comes attached to the rear derailleur,
meaning whether internal frame wiring is necessary or not.
However, the point that the rear derailleur and shifter connect wirelessly is the same.

The new GRX, which has the battery on the rear derailleur,
has compatible sprockets
only in Microspline 10-51T,
but if you want to use MTB 9-45T,
you can switch the rear derailleur to the GS (mid-cage) of new XTR or new XT
to make it compatible.
(New Deore is available only in SGS (long cage),
with compatible sprockets only in 10-51T).

So within the conditions of
front single-ring and rear hub being Microspline
with sprockets only in 10-51T or 9-45T,
you can use 12-speed road STI levers
with new XTR/XT/Deore/GRX rear derailleurs to
solve the problem of pulley cages rubbing the ground on small-wheeled bikes,
or realize Shimano component road bikes without shift-related wiring or internal components in the frame from the start,
and similar applications become possible.