Why does it need to be an app then? And why one server?
Literally, what you’ve described is the www. The browser is your thin client. It connects to not one but many millions of servers and is able to use their resources to run queries, access menus, place orders. All that jazz.
Oh, and with the ridiculous advancements in technology, streaming services and games work amazingly too! Video streaming is so well studied that every Tom, Dick, and Disney has started their own streaming service and is charging through the nose for it. Every year, folks get arrested for running Plex servers or IPTV with millions of hours of pirated content that is used by thousands of their happily paying customers (more happy than Disney’s customers).
And Amazon Luna and Xbox and PlayStation have all shown how game streaming can be so easily done over HTML5. The only blocker on making that the default way of gaming is Apple’s greed. Not that it’s a good default. There’s something to be said about mobile hardware and chip design that has made amazing advancements in the last few years in the GPU space, making on-device processing really worth it.
Don’t remember what it’s called but there’s an internet law - that any advancement in hardware will immediately be offset by more expensive software requirements which will consume more of those resources. Looking at you, Chrome. Also looking at you, react framework.