Using Google Maps
Google Maps is a popular pay-as-you-go tile provider solution, especially for large commercial applications.
Unfortunately, Google Maps does not officially document - and therefore support - a static raster tile server. There is an open and free endpoint (findable by doing a small amount of digging online), however, it violates their terms or service for the Google Maps API Platform, so it is not shown here.
To use Google Maps properly, you will (unfortunately!) need to use the official Flutter package.