Samsung
Change Preferred Network Mode auf Samsung
Network mode tells your Samsung phone which mobile standard to use for calls and data. Depending on the model and carrier, the options range from 2G and 3G up to 4G (LTE) and 5G. Forcing an older standard like 2G reduces data speed drastically and can also block features that rely on 4G, such as VoLTE for HD calls.
Locking the mode to a single standard makes sense in rare cases, for example to save battery in an area with no reliable 4G coverage. In most situations the automatic option that includes the fastest available network delivers better performance and should stay selected.
On dual-SIM devices, SIM 1 and SIM 2 each have their own Network mode setting, so check the correct slot if only one number has connection issues.
Menu path
Open Settings ➔ Connections ➔ Mobile networks ➔ Network mode SIM 1 / 2 ➔ choose the desired option from the list.
If the phone still shows no signal or drops calls after changing this setting, the cause is usually coverage or a SIM/APN problem rather than the Network mode itself.