Activate "double tap to lock screen" in the KISS settings: Settings> User Experience> Gestures> Double tap to lock screen.
If you now double-tap on the screen, a pop-up dialog opens with the following note:
"Double-tap to lock needs the Android Accessibility API. No data is processed, no data is stored. To use this feature, enable KISS in the following screen."
Click on "OK". This opens the devices's accessibility menu.
Tap on KISS launcher then select use KISS launcher
A warning pops up:
Allow KISS launcher to have full control of your device
...
with a note on what the app can do having access to Accessibility API:
- view and control screen
- view and perform actions.
Confirm with allow.
The "double tap to lock" gesture now should work.
If you want to withdraw KISS's authorization, you can do this via the GrapheneOS settings - Settings> Accessibility> KISS launcher.