We have a built-in Grpc Protobuf generator under Window/UnityGrpc/Protobuf.

By clicking it, you will open the Protoc Generator Window Below:

Download The Grpc Protobuf Generator Tools:
Github Website https://github.com/protocolbuffers/protobuf
Or Our Pre-download Version
https://drive.google.com/file/d/16beDi2EayAqhAGMWMXJg1eKJwvrqMeMP/view?usp=sharing
Enter The Absolute Path For Grpc Plugin.exe and Protoc.exe
Put your .proto file inside the Unity Assets folder.
Click ‘Compile .proto Files!’ Button.
It will scan all the .proto files inside Unity folder, and start generate the Grpc Class.
If Auto Compilation Protobuf is enabled, it will auto compile the .proto files.