Thanks for posting! We’re actively working on iPhone Duo support, and this should be fixed in the next version of Mlem. If you join the TestFlight, you’ll get the changes sooner, possibly later this week: https://testflight.apple.com/join/W6ajfKQt
Apple’s frameworks do a lot of the layout adaptation automatically, including the tab bar orientation. It’s laid out wrong because we’re still building on Xcode 26, and Duo support is part of Xcode 27.1. There are a handful of things we need to fix manually, though, which are tracked on GitHub here: https://github.com/mlemgroup/mlem/issues/2976
If you encounter any further bugs, please let us know! You’re the first Mlem Duo user I’ve seen thus far :)