I have after much trial and error. I do not have a public example but add these jars to your job:
MyProtobufMessage.jar
chill-protobuf-0.10.0.jar
flink-sql-protobuf-1.16.0.jar
and then add this to your create table API:
'format' = 'protobuf',\
'protobuf.message-class-name' = 'mypackage.MyClass$MyMessage',\
'protobuf.ignore-parse-errors' = 'true'\