This would require the main proxy running as root or with some other sort of elevated privileges to allow cross-user network access though, right? If so, wouldn’t that essentially make the user-specific reverse proxy unnecessary in most cases?

I think this is what OP was originally trying, but this approach breaks when each service’s Podman service runs on its own localhost user.

This is due to a security design deicison of Podman. Each user’s network(s) is only available to that user. This is great for most services, but can cause issues for some services - especially reverse proxies. Unfortunately, I’m not aware of an ideal solution. The only solution I’ve seen is moving the reverse proxy to another host and exposing the services’ ports on the localhost. I hope someone can provide a better solution!