When you open the theme in the substrate application, you will see the drop-down menu above the overlays. You must choose a function from your Android ROM version. There are also overlays with different variants for the specific Android version.
Some applications like PSBA Clock, Mail, and Gallery may or may not work, because each custom ROM has its own variant of these applications, so if you get an error while compiling, just do not install them.
Supported Android
{7.0 and UP}
Supported Android Version:-
Nougat (7.0 – 7.1.1) – Oreo (8.0-8.1)
Download Belo substratum 8.4 Patched APK For Android