Incoming MMS messages are automatically downloaded to the Oppo smartphone. Depending on the tariff, this may incur additional costs, but the automatic download of MMS messages can also be deactivated.

Android 10 | ColorOS 7.0
Step 1:  Open the  Messages -App
Step 2:  Open the  Menu
Step 3:  Tap on  Settings
Step 4:  Tap on  More settings
Step 5:  Tap on  Auto-download
Step 6:  Enable or Disable  SIM1  /  SIM2
  1. Open the Messages-App
  2. Open the Menu
  3. Tap on Settings
  4. Tap on More settings
  5. Tap on Auto-download
  6. Enable or Disable SIM1SIM2

Oppo Instructions