For your projects to appear in Finder, macOS requires you to enable the Companion extension once. It's the same permission that Dropbox or Google Drive request.
How to enable it
- Open System Settings.
- Go to General → Login Items & Extensions.
- Find File Providers and enter.
- Enable the Companion for Basecamp toggle.
What happens next
Once you enable it, your projects appear as folders in the Finder sidebar, under Locations. Enter any of them and its contents will list automatically.
Note: without this permission, the app continues to work (Launcher, menu bar, etc.), but your folders won't be visible in Finder. If you've enabled everything and they still don't appear, check "Troubleshooting".