Hello,
After reading the above post, i am contacting you as I get the same error.
the frontpage is not loading the map and the backend is also not loading the map.
the javascript error in the Chrome console shows
util.js:233 Google Maps JavaScript API warning: RetiredVersion https://developers.google.com/maps/documentation/javascript/error-messages#retired-version
Joomla is last update 3.9.15
I revert the template to protostar and test, but same issue
this is the frontpage
http://www.jakana.be/index.php/fr/distributeur-plumka

I attach both screen capture

Thanks for your help

Pascal