The font is set during the OnePlus smartphone setup, but can be changed later without resetting the device.

The following fonts are available for selection by default:

Android 10 | OxygenOS 10.0
Font style -  Open the  Settings
Font style -  Tap on  Customization
Font style -  Tap on  Font
Font style -  Choose  Roboto  or  OnePlus Slate
Font style -  Tap on  Save
  1. Open the Settings
  2. Tap on Customization
  3. Tap on Font
  4. Choose Roboto or OnePlus Slate
  5. Tap on Save

OnePlus Instructions