Dammit, Apple. When we all hoped that the idea behind iPadOS was that it'd permit differentiation between the platforms, this was not what we had in mind.
Yes, it's an incredibly trivial, even frivolous, feature and yes, other platforms have had similar visual effects for years so it's not as if Apple have led personal computing towards some new frontier here. The point - as with last year's failures to expand on widget placement on the iPadOS homescreen and bring the App Library to iPadOS - is that it looks as if creating iPadOS meant formalising the iPad's place one step further back in the queue for features than iOS.
Not that anyone was in any doubt that was the case, but formalising the ranking of the platforms like this two years running is just depressing. This is a rare case of Apple adding some old-fashioned quirkiness to their platforms again, and it's astonishing that the iPad misses out on it. I'd be amazed if there was some deep technical reason why this app couldn't be brought to iPadOS at the same time as iOS, and even if there is one I suspect ultimately it's driven by Apple choosing not to expend the time and effort to make it happen on iPadOS.