You can initiate a Stripe payment from a tRPC procedure, or call a Stripe API, and you can do that from any part of your backend code.
The webhook on the other hand, is a specific format over a REST API. You won't be able to listen to Stripe events/callbacks with a simple tRPC procedure. It's just not meant for that. Even with middleware, etc, I would not recomend to try to setup a tRPC procedure for that...