Oppo
Enable Mobile Data During Calls on Secondary SIM auf Oppo
On dual-SIM Oppo phones, one SIM usually handles voice calls while the other can supply mobile data. If that second SIM is not allowed to stay active during a call, your internet connection drops the moment you answer the phone.
Coloros keeps this behavior behind a dedicated switch instead of tying it to your default data SIM choice. You control it under Settings ➔ SIM card & mobile data ➔ Enable or disable Use Internet during calls on secondary data SIM. Turning this on tells the system to keep routing data through the secondary SIM even while the primary SIM is busy with a call.
This only works if the secondary SIM actually has an active data plan and network coverage. If data still fails after enabling the toggle, check whether the secondary SIM's network mode supports data alongside voice, since some carrier combinations restrict simultaneous voice and data on certain bands.
Turning the switch off is useful if you want to save mobile data or battery during calls, or if your carrier charges extra for data used on the secondary SIM. Leave it disabled if you never browse while on a call.