API level 23 and above are supported. If you want API level 21~22 support, use 1.3.x LTS series. ARM64 required. If you want 32-bit support, use 1.3.x LTS series. NDK ...
Custom ROMs are open-source Android OS’ each with pros and cons. Although most custom ROM projects have faded over the years due to Google making it hard for them to survive, a few are still active.