Question About UNITY_64

Hello. I have one simple question about Unity. I need to use UNITY_64 so that I can compile my source code and release it as a android apk. my code looks like below.

#if UNITY_64
private string libName =
private string libName =

but the problem is … in the built app, it does not seem to work the symbl (UNITY_64).
because the libName was event I built the app after setting target architexture as ARM64 in player setting,

I searched about it on the internet and someone says that UNITY_64 is only working for unity, not for real app like android and ios.

is it right?

if I want to compile my code like below… what should I do…