EDIT: Other people are using BC PC fine with satellite imagery... anyone else having a problem?
This has seemingly changed from recent years, and weirdly enough Basecamp Mac allows the install but Basecamp PC doesn't.
So if you have an existing subscription, be careful. Seems you need to use a Mac now to upload the imagery to the watch. I only found out when using Basecamp PC (which tells you) whereas Basecamp Mac not only doesn't tell you, but allows the files to copy over.
Surreal? It sure is.