Hey did you find a fix? I can't find any at all so far.
Viewing post in error:json-rpc error 9000 problem
I don't know about anyone else, but on MacOS, I had to turn off iCloud Private Relay; if you're not using a Mac, check if you have any proxies, relays, VPNs or similar, and see if briefly disabling those helps. (If that works, the next step would be to create an exception specifically for the blocked Itch hosts.)