I am using the app on Android (latest) (Pixel 6 Pro) and the system buttons can be made visible when gently swiping up from the bottom edge.
In the settings you can activate "Enable Vertical Video", when flipping the phone to landscape mode, the overlay stays in portrait mode, but the video is in landscape mode anyways.
In the camera, tap on the rectangle with 4 corner inside and in the appearing bar you can tap on the middle icon that looks like a letterbox, there you can change the recording size.
Hope this helps out.
EDIT: I found a screenshot with the icons you have to tap for resolution.

- Screenshot 2024-12-19 133056.png (194.44 KiB) Viewed 906 times