There is still transcoding done thru the server, maybe depending on the app but the ones that use livekit it would.

Hosting costs money, maybe if you disable voice, video, uploads, and only allowed text it would be manageable but discord is free. I run my own chat server but it’s only for like 10 people.

Autofill, easy sync, password generation, browser extension, mobile app, ease of use to name a few.

Yeah, maybe it’s because I run public sites on kubernetes at work that I’m not as scared but a good locked down network is fine. Thousands or businesses run public URLs, as long as you configure it right you are mostly good. There is always a risk of vulnerabilities in the software for immich, your proxy, your auth provider so doing it that way increases your attack surface than just the VPN.