I'm happily using Phoenix+LiveView for a website that works as a PWA. This also includes offline mode with sync-when-internet-is-available functionality (thanks PouchDB!). This covers online/offline/mobile usecases, with no explicit RPC, and no requirements for the end device that the app would run on, other than a _capable_ browser.
(Admittedly, browsers on iOS are gimped, but that's part of the Apple tax).
(Admittedly, browsers on iOS are gimped, but that's part of the Apple tax).