FWIW driving last week in a southern European country I came across a newish (as in roughly a year old) road segment that Telsa navigation doesn’t have and which is present in both OSM and google. Unluckily both Here and Tomtom are currently missing the road which means it doesn’t really help with deciding what they are using.
In general though whatever they are using for navigation there has lousy geometry in numerous places. That is easily visible as the navigation route indication varies considerably from the gmaps display.