I think Garmin express is now just for connecting and we are supposed to use Garmin connect. But I may be wrong.
On a PC, Back In The Day, you would upload your rides to the Garmin Connect website.
There was an Upload button, and you browsed to the Activities folder on your device.
This was not seen as the 'modern' way; having to browse a file system!
They wanted it to be plug-and-play, it just works by magic.
Hide the file system! There is no file system!
So some years back, they updated the website to the 'modern' theme, and the Upload button was gone.
You were meant to use the Garmin Express software, which was always running in the background.
As soon as you plugged your device in, this would automatically 'sync' everything on your device to the Garmin Connect website.
This caused a bit of a fuss, for 2 reasons:
1) You could not upload arbitrary .fit files;
2) Privacy: it would upload *everything* on your device, whether you liked it or not!
So they eventually relented, and put the upload button back on the website, where you can browse to the device and select what you want to upload.
I think they still 'prefer' that you use the Garmin Express utility to automagically sync, but they can get in the sea.
This is how I use my Garmin devices.
I no longer have Garmin Express installed, and do all my uploading by selecting the files I want using the website and browsing the device.