Reddit's app registers itself as a uri handler for reddit links but (thanks to google) AMP or iframe results don't prompt the actual system uri handler that would take you to the app.
Whoa, is that what this is? I’ve been wondering for quite some time why in the world Reddit hasn’t figured out how to make the “open in the app” links actually work. It’s bonkers that they spend so much effort making the web site push you to the app, but don’t even provide a working way to open a piece of content in the app.