The black bar in landscape mode is definitely related to the camera notch / cutout.
This screen cutout isn’t configurable on my Motorola phone, like on other phones.
cutout options
In developer mode, I can choose several cutout options. Unfortunately, none of them corrects the black bar.
The default cutout is the “best” option, the others add black bars in portrait mode or landscape mode.
There’s a “waterfall” cutout which removes the black bar in landscape view, but adds two bars on top and bottom (landscape mode), thus reducing the max height. And in portrait mode the same waterfall cutout adds two bars on the left/right, thus reducing max width.
Solution
The solution would be to add a “fullscreen” parameter to Obsidian. Each and every app needs to add fullscreen on its own, because fullscreen isn’t available globally
At least on my phone, there’s no visible or invisible app I could activate to control global fullscreen.