Only Google Android, neither my current nor my previous phone have had the option to use instant apps.

Maybe it's a region lock thing (I'm not in the US) but it's not globally available on all Play Services devices so I don't know what the point of putting effort into Instant Apps really is. It only makes sense to support all of Google Android or none of Google Android.

Not similar. It is absolutely the same.

It’s great to see that that’s already supported! I wasn’t aware of that, and it’ll allow Google to pivot this feature towards a similar use-case.

Right now however it seems to primarily be marketed to mobile game developers.