I am a little bit late but I have faced the same problem trying to expose thanos-sidecar service to a remote Thanos querier.

Thanks to your help I managed to make the grpcurl list to work but unfortunately on the querier side I still have this error :

• update of endpoint failed" err="getting metadata: cannot obtain metadata: neither info nor store client found" address=mydomain.com443

Did you find a way to make it work end to end ?