How to check the current platform of Android OS?
If you have adb set up, it's a one-liner at the shell prompt:

$ adb shell "getprop ro.product.cpu.abi"
arm64-v8a


In this example, the device asked answered that it has a 64bit ARM V8a CPU (second line).

Note: You can also run the quoted command in a terminal emulator running on the device / emulator. In there, it's just getprop ro.product.cpu.abi.