If you go into FME Options>Background Maps you can then add a new background map from a source. Entering any required information. Once added there is a drop down option in the Graphics Viewer where you can select from added background maps and add new ones. Similar process if you are using Data Inspector.

There’s a help document on adding your own here: https://docs.safe.com/fme/html/FME-Form-Documentation/FME-Form/DataInspector/Background_Map.htm