You have no local network access to it at all? (WOL will work across the subnet, you don’t need to connect directly to it)
If genuinely not (and I’d be surprised if that is the case) add another nic of any sort (cheap) for WOL, or use something like Switchbot?
I don’t know what prosody is, but my go-to for hosting anything behind a cgnat that needs incoming connections is to use cloudflare tunnel. Free, reliable, lightweight.