Have you tried using a derailleur extender? I was about to pick up a Garbaruk cage (copy) for my GRX 812 RD, because I was having so-so shifting performance with my ZTTO 9-46t. I remembered I had a Goatlink in a drawer, so installed it. Now shifting is much better (about 85-90% compared to stock), enough so I don't feel the need to buy the Garbaruk cage.