Very few phones have "Dual SIM Dual Active/Dual SIM Full Active" which is required for both SIM to work at the same time.
Our phone and most others use Dual SIM Standby, meaning that If you're on a call on SIM 1, then SIM 2 will be dead, regardless if Dual SIM 4G is enabled. What this option does is that it will listen on 4G with both SIMs when in standby. If disabled, SIM 1 will have 4G VoLTE and SIM 2 will only have 3G. Both will have 4G data without Dual SIM 4G so this option is only helpful for those who have carriers with VoLTE support on ASUS devices.
