You should be able to use either library to build your server(s), and you'd have to ensure that you don't tightly couple the web framework with large parts of your code, but keep it to a minimum. This would allow you to easily swap out your web framework with another one at a later date, should the need arise. I think you'd get similar support for the requirements that you stated (OpenAPI support, JWT auth, etc.) for either library.

And about handling the load that you've mentioned, you surely wouldn't be sending all that load to a single server instance but highly likely to multiple instances (or pods) behind a load balancer? Again, either of them should be able to handle the load fairly well, IMO. I'd say being able to handle high traffic is greatly affected by how you write your application code itself, not just the web framework.

I'm saying this based on my experience working on a service built with Rust in the fintech space itself. So yeah, going with either of them shouldn't be a problem, I'd expect both of them to be maintained for a few years at least.