I just located the extension. Rather than being list on the extension drop down, it was placed at the bottom of the tools drop down which is a bit confusing.
It’s a good idea when installing extensions from the Extension Warehouse to scroll down a bit to read instructions and such. There’s information about where you’ll be able to access the tools and also if there are any required support files needed.
This is a bug. The Extensions panel of the Preferences dialog was moved to it’s own Extensions Manager dialog with the 2017 release.
So this informational messagebox you see (in versions greater than 2016,) should have been revised so that the 2nd sentence reads, “To load the extension go to the Extensions Manager window and check the box next to the extension.”
@thomthom, can you check to see if this issue has been logged internally for the Mac builds ?