We can sort the contacts displayed in the Contacts app on the OnePlus smartphone by the first name or last name you have saved, if desired.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Contacts app
Step 2:  Open the  menu
Step 3:  Open the  Settings
Step 4:  Tap on  Sort by
Step 5:  Choose  First name  or  Last name 
  1. Open the Contacts app
  2. Open the menu
  3. Open the Settings
  4. Tap on Sort by
  5. Choose First name or Last name 

OnePlus Instructions