And reset the camera:
>>> url = "http://192.168.1.1/osc/commands/execute"
>>> payload = { "name": "camera.reset"}
>>> r = requests.post(url, json = payload)
>>> print(r.status_code)
>>> print(r.json())
200
{'name': 'camera.reset', 'state': 'done'}
The camera did its red and blue LED blinking activity. After that, camera photo self-timer activation works again. Turning on the camera with the Wifi button pressed results in a green LED for photo mode.
Thanks, @codetricity for the hint.