You can make calls to tRPC endpoints from anything that can send an HTTP request. The RPC format for requests might not be your cup of tea, but it works.
Ostensibly, the product isn't as useful as the existing gotos (json schemas, shared libraries, graphql, etc), if you cannot create a shareable schema for validation. The ability to form arbitrary requests is already assumed. If your messages are very complex, you need some tooling.