That’s because they didn’t make an iPad app and so it was just the iOS app on a large screen. Lots of app used to be like this until they made iPadOS versions.

Looks like nothing has changed. This is how it opens up on 4k screen. Although, it looks like they tweaked it a little. Up until recently I remember opening a post would show a hilariously small like 800 by 600-something box, half of which was comment section that'd fit like 5 comments at best. But now they finally made it properly scalable.