Handle unsupported URIs with the system handler
I'm sorry if this is a duplicate; I actually thought I posted this as an issue but it turns out I just thought I did. I looked around for a duplicate but couldn't find anything, so I'm posting it now.
It seems that Epiphany just silently drops requests to open unsupported URIs instead of redirecting them to the system handler. Apps register special protocols with the system to open themselves, and then websites can use these protocols to open the app. This is commonly either used for sign-in (the app opens a browser to log-in, and then the browser tries to open an app-specific URI to send back an auth token) or to launch apps like Zoom.
The zoom issue is actually extra annoying; Zoom uses the browser for enterprise sign-in, and also to launch meetings. I'll often get emails with links that take you to a landing page that tries to launch a zoommtg://....... link. On Firefox, these pages trigger a prompt that asks what to open the link with. Epiphany, on the other hand, does nothing. My university also configured Zoom to forcibly sign me out if I've been inactive for 15 minutes, so I run into this a lot trying to sign back into Zoom.