We can set the default account for newly created contacts on the OnePlus smartphone so we don't always have to manually select the desired location during creation.

Once set, the new contacts are automatically stored in the desired account until this is changed.

Note: To temporarily change the location for new contacts, the account can be manually selected at the top of the screen during creation.
For example, if multiple Google accounts have been linked to the OnePlus device, all accounts will be displayed as possible contact stores.

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  Default account for new contacts
Step 5:  Choose an  account
  1. Open the Contacts app
  2. Open the menu
  3. Open the Settings
  4. Tap on Default account for new contacts
  5. Choose an account

OnePlus Instructions