eject

If you don’t see some Garmin item mounted in the Finder sidebar, and if there’s no eject in the Garmin app, contact Garmin support. Seems this is a common question with Garmin devices too, and with no obvious answers.

Closest I can find is very old:

https://discussions.apple.com/thread/4046014

If you can see the device in the Finder sidebar or in Disk Utility, then there’s (usually) an eject option:

Use external storage devices with Mac - Apple Support

glosally wrote:

I have the new garmin gps plugged in. can't find how to eject it to unplug. there is nothing anywhere that says garmin.

For your third party plugin I would query Support/Help/FAQ/Known issues/compatibility/uninstall

and see what the developer has to say:

https://support.garmin.com/en-US/ql/?focus=topics

https://software.garmin.com/en-US/gcp-faq.html