I’m not sure about this, we already support resizing on our app for a while now because of our iPad/mac catalyst version, so I fail to see how different it would be on the Duo.
I assume other apps will have have the same, since our team is super small compared to everyone else.
Apps not rebuilt with the latest SDK will display in pillar-boxes mode, centred on the screen.
The small screen is so small they had to move controls to the right, I would expect glitches because of that, especially for custom controls.