https://www8.garmin.com/support/download_details.jsp?id=14933
You need something like this: https://www.android.com/filetransfer/
Watch shall be set on MPT. Tha's a new "feature" since the Fenix plus series (and other) last year. No USB device anymore in the native sense...
It's actually related to music on watch. The watch looks like a media player, and Apple only recognises their own.
Windows and Linux don't require anything special.