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.