Protobuf files are best added manually in csproj (can decide what exactly gets generated+Include as Link).
Do not care about InteliSense mentioning errors. The base classes will get auto-generated on usage anyways.
endpoints.MapGrpcService<GreeterService>(); in Startup, otherwise APIs are not exposed.
import 'bla.proto' in protocol buffer definitions does not work :(. Report bug!
The types are hard to mock. Also, setup is not really that DI-friendly. Should report a bug/design discussion point with AspNet.Core team.