For Firefox this exists, all other browsers have this functionality directly implemented. Chromium-based browsers can usually be started with parameter --app=https://example.com to start example.com in a SSB/PWA-looking window.
Plus: With this you do not lose the ability to open links in new tabs and you have access to your default configuration for websites.
Way better than the overcomplex “Firefox PWAs” I suppose.
Yep. Technically it just creates a new tab that creates a popup with the requested URL and the created tab closes itself after the popup was created. So not really a PWA but just a popup with a website in it, but in most cases this is absolutely fine since you're online anyways, and modern browsers are good with caching.
Yes, this is not a PWA system but an SSB implementation. In the context of this thread it's fine since Lemmy is useless without Internet connection, so why bother with persistent local storage and not just rely on browser cache?
On Linux you can create a simple .desktop file and place it where your system can load it. It will be automatically placed in places where your other application's desktop files are shown. On Windows you can create a shortcut and change the shortcut's icon and place the shortcut file wherever you want.
I use this technique on my private Linux machines as well as on my work laptop (Windows 10).
Persistent local storage is a question of scale. For example having old posts and comments cached, or the entire UI. It would just load faster and save tons of duplicated data that is always the same but downloaded over and over again.
Yes I know how to create the entry. Not sure about the menu chapter, but these are very possible.