Synchronization with Google CalDAV/CardDAV is not officially supported by Google or DAVx⁵. For some people it seems to work, for others it doesn’t. Google officially requires OAuth 2, which is not supported by DAVx⁵.
We have received updated information about Google CalDAV:
The old endpoint https://www.google.com/calendar/dav is deprecated and no longer supported.
Now you shout suggest https://apidata.googleusercontent.com/caldav/v2/calid/events
Please have a look on https://developers.google.com/calendar/caldav/v2/guide
Google Account security:If you use 2-Step-Verification for your Google account (recommended): Create an app password for DAVx⁵ and use the app password for signing in with DAVx⁵. If you’re not using 2-Step-Verification: To allow Basic auth clients like DAVx⁵ to connect, you need to “Allow less secure apps” in your Google account before setting up DAVx⁵.
If you have further information, please just post here.