OnAirScreen is (for now) a 32bit (armhf) Application only.
If you want to run OnAirScreen on a 64bit (aarch64) RaspberryPi OS installation, you need to add some libraries manually.

$ sudo dpkg --add-architecture armhf
$ sudo apt update
$ sudo apt install -y libc6:armhf zlib1g:armhf libgles2:armhf libxcb1:armhf

After installing those libraries and their dependencies, you should be able to run OnAirScreen.