I’ve just fitted GRX810 levers. The reservoir/bleed screw is larger than the old 5800 levers I removed, you’ll need a different bleed kit. I got one from Epic Bleed Solutions that has an adaptor that fits both. I also got litre of mineral from halfrods. Used about 30% of it.
They are a pia to bleed. Saying that, the Ultegra caliper was fine but the new Grx810 caliper took work. Good luck