tRPC is not at all intended to ever be a public API, the way REST or GraphQL is. It's meant to be a tight, private connection between your client and your server.

If you use tRPC in your stack but want a public API, you will almost certainly need to build that out separately, via traditional REST, or GraphQL, or maybe gRPC. This feels all kinds of wrong initially, and there are some obvious and not so obvious disadvantages to this, but honestly it's not all bad when you get down to it.