I have bought new smartphone - Redmi 9A, but it is not supported. Its hardware is good, so maybe Im doing something wrong?
Infinite Flight requires a device with a 64bit processor and Android 7.0. While your device might have a 64bit processor installed, it is still possible that Xiamoi is running it with a 32bit Android version.
You can check this by downloading the free app AIDA64 from the play store. Take a screenshot from the CPU page and post it here. We will then know for sure what Android version your phone is running!
Unfortunately that device model is in fact running a 32-bit version of Android.
Thanks! As mentioned by schyllberg already, your device is, unfortunately, running a 32-bit Android version. As Infinite Flight requires the 64-bit version, unfortunately, your phone is not compatible.