While this isn't specifically an issue for MODX Cloud, we do see a number of customers who have run into the problem of their Google Maps suddenly no longer working.
Google Maps Changes
Starting in 2018, Google changed the way they allow site owners to use Google Maps in their sites. And, recently, they completed the transition to the new system and you are now required to have a billing account set up with Google Cloud. For the vast majority of site owners, Google Maps will remain no-cost. Google provides a $200 monthly credit and it takes a significant amount of traffic to go over that $200.
Verify the Cause
To be sure this is the issue, in your browser, you can use your Web Developer tools Java Script Console to see the error message that Google displays if billing is the reason it has failed.
To find your developer tools in your browser, see this article by Balsamiq on Finding Your Browser's Developer Console.
Get it Working Again
As always, if you need us, please use the Help button in the MODX Cloud Dashboard and ask for assistance.