SIM cards can be activated or deactivated on the Oppo Smartphone independently of each other. For example, to be unreachable on a SIM card, it does not have to be forcibly removed from the device. To do this, it is sufficient to activate (or deactivate) the switch in the settings.

Android 10 | ColorOS 7.0
Step 1:  Open the  Settings
Step 2:  Tap on  SIM card & mobile data
Step 3:  Choose desired  SIM card
Step 4:  Enable or Disable  Enable
  1. Open the Settings
  2. Tap on SIM card & mobile data
  3. Choose desired SIM card
  4. Enable or Disable Enable

Oppo Instructions