Oppo
Change Preferred Network Type auf Oppo
The Preferred network type setting controls which mobile network generation your Oppo phone tries to connect to first: 2G, 3G, 4G, or 5G. Android and ColorOS hand this decision to the modem, but the setting itself decides the search order and whether older networks are allowed as a fallback.
Forcing a phone to 5G-only in an area with weak 5G coverage often results in no signal at all, since the device won't fall back to 4G. Setting it to a lower mode like 4G can help stabilize the connection in rural areas or save battery, but it blocks faster speeds even when 5G is available nearby.
Where to find the setting
Open Tap on Settings ➔ Tap on SIM card & mobile data ➔ Choose a SIM card (Dual SIM) ➔ Tap on Preferred network type ➔ Choose an option.
On dual-SIM devices, the setting applies separately to each SIM, so check that you picked the right card before changing anything. If a network mode is missing from the list, your device hardware or your carrier's SIM does not support it.