Oregon 700 not connecting to Basecamp

I have a Garmin Oregon 700 running version 6.0, a 2009 Mac Pro running El Capitan, and a 2014 MacBook Pro running Big Sur. 

Garmin Express running on either computer connects to my Oregon 700 and updates the software.

Garmin Basecamp doesn't connect to my Oregon 700 from either computer.

On my MacBook Pro, Basecamp 4.8.12 shows the Oregon 700 under My Garmin Devices. If I select an adventure and View > Show Selected Data on Map, some routes appear but others have a spinning black wheel next to the filename. When I try to upload a GPX track from my computer to the Oregon 700 nothing happens.

On my Mac Pro, BaseCamp 4.7.0 opens and displays Task Launcher and the spinning beach ball. Force Quit shows that BaseCamp isn't responding.

How do I get my Oregon 700 to work with Basecamp?