To solve this you have to edit framework/php/class-gmaps.php
In my Version 4.5 line 17 to:
const API_VERSION = ‘quarterly’;

After this i can add and save api key in enfold settings successful an my map is loading correct.

@Team Kriesi:
Can you change this line from old Version 3.3.0 to “quarterly”?
Would be nice if it persits an update.