It needs to be done in each app, by bypassing the system web browser or maps support. So Google may support it in their apps, but Apple doesn't in the system apps like Siri, Contacts, etc.
Yea I was very pleasantly surprised to see this worked when I switched back to ios from android. It allows me to stay within the google maps, gmail, and chrome ecosystem most of the time.
But that's only from within the Google ecosystem. Click on on a link in a non-Google app and you won't see Chrome as an option.
Well, you actually _will_ in quite a lot of apps these days, which is really a symptom of the problem.
I think Google has an SDK to allow other developers to do this on iOS. Unfortunately I don't think many iOS developers know or care.