You can certainly do it, and sometimes it works out just fine, but generalizing all popular software client/server architectures contribute to modern software woes in my opinion (not to mention it discourages privacy! your tailnet example being a good counter-example).

Cross-platform development is another can of worms, and a strong advantage of the web for software distribution. There's a lot of snake oil - like SwiftUI, React-Native, Flutter, that always gets people excited but rarely makes an appearance in world-class software.