I wonder if that’s an iOS and Safari thing. It’s always been my understanding (with chrome and android anyway), that once the original install popup is displayed and dismissed by the user, then it’s impossible to trigger that popup again without the end user clearing their cache. A website can be set up to suppress that popup and display it later through a user action, but it’s still a one and done deal…unless something has changed with PWA’s recently. For that reason, I’ve thought that it’s an odd addition to the side menu. When I tested it a while back I couldn’t get it to work either. It just doesn’t make sense to me how it could work based on past experience.
Don’t get me wrong though, I think an install option in the side menu would be awesome for PWA’s (if it worked), but I don’t see how it could ever work properly under these circumstances. I think it’s largely the browser that prevents these install or notification popups if a user rejects them initially. Otherwise some websites would abuse the privilege and would be persistently trying to get you to install their PWA or accept notifications. The browser protects the user by showing the option once and if they don’t want to see it again, they won’t.