We all know whenever discussion of protobuf comes, it's almost always along with grpc. But its just a data format, that can be used anywhere. Here are ways how we've used it https://blogs.lupyd.com/blog/protobuf-everywhere/

storing the wire format in databases, using it as replacement for jwts, client-to-server operations as well. The way protobuf is encoded comes in hand a lot more than we realise, working with json all day.