Well, OP was the one who suggested to build a Reddit clone, my side project is something else :)

re: gRPC, largely pragmatic because of familiarity with protos and RPC interfaces defined in terms of protos. I wanted a typed API definition that generates first-class implementations in Typescript and Python.

Haven't had much success in the past re: using other formal mechanisms of defining API interfaces, and I'm no longer up-to-date with what's recommended in this space (any suggestions).

Alternative was GraphQL (since using React) but that's a learning curve and dealing with protos in Typescript and Python is a known-known for me.