If Dual SIM is used on the OnePlus smartphone, one SIM card can be deactivated if desired.
Any priorities or settings for accessing mobile data or sending SMS are automatically transferred to the other SIM card.

When a SIM card is deactivated, no calls or SMS messages will be received.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Settings
Step 2:  Tap on  Wi-Fi & network
Step 3:  Tap on  SIM & network
Step 4:  Choose a  SIM card
Step 5:  Enable or disable the  SIM card
Step 6:  Confirm with  OK
  1. Open the Settings
  2. Tap on Wi-Fi & network
  3. Tap on SIM & network
  4. Choose a SIM card
  5. Enable or disable the SIM card
  6. Confirm with OK

OnePlus Instructions