https://stackoverflow.com/questions/50929198/open-installed-pwa-from-external-url

For iOS, there is actually a very unknown way which you can install a .mobileconfig profile which installs a web clip (or multiple web clips if you like).

This will run your website in fullscreen and is very similar to how iOS PWAs work. You can also link to it online or send it as an Email attachment for your users to install.

Just make sure you add this for the webpage to open fullscreen:

<key>FullScreen</key>
<true/>

You can read more about creating your own from scratch here:

https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/iPhoneOTAConfiguration/ConfigurationProfileExamples/ConfigurationProfileExamples.html

or if you have a Mac you can get the "Apple Configurator 2" App:

https://apps.apple.com/us/app/apple-configurator-2/id1037126344

or you can take the easy route and use a generator here if you don't have a Mac: