If we enable this feature on the OnePlus smartphone, an additional symbol is displayed on the keys, which inserts the alternative character by tapping and holding the corresponding key, without having to switch to the symbols keyboard layout.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Settings
Step 2:  Tap on  System
Step 3:  Tap on  Languages & input
Step 4:  Tap on  Virtual keyboard
Step 5:  Tap on  Gboard
Step 6:  Tap on  Preferences
Step 7:  Enable or disable  Long press for symbols
  1. Open the Settings
  2. Tap on System
  3. Tap on Languages & input
  4. Tap on Virtual keyboard
  5. Tap on Gboard
  6. Tap on Preferences
  7. Enable or disable Long press for symbols

OnePlus Instructions