Unable to view iTunes Library

I had a similar issue and have read the suggestions on this forum, trying out the symlink to the library on another partition (which is also a physical disk), where I keep the iTunes library file and music. Library and songs never appeared in Garmin Express, version 7.10.0.0.

But then I figured it out with trial and error of setting up a fresh iTunes library first on c:\, then on d:\ (different partition, same drive), then e:\ (different drive then one with c:\ and d:\). The problem wasn't the location, but something faulty in the iTunes library which caused nothing showing in GE.

To clarify - iTunes Library location is set by setting the Location for the "Music" Library folder that comes with Windows. It's in c:\Users\<username>\Music\ by default, but you can set it on another partition/drive. If you set it to "d:\Music", iTunes library will be in "d:\Music\iTunes\". Make sure this folder location is set! How to do it: https://winaero.com/move-music-folder-windows-10/#:~:text=Windows%2010%20stores%20your%20Music,in%20File%20Explorer's%20address%20bar. , you don't need to move the files though, better to do it manually. 

Then:

- exporting playlists of the current library,

- making a completely fresh library (you can just delete the iTunes folder, caution if you have the option selected which imports songs into the same folder though - or just delete the "iTunes Library.itl" file) - after restarting iTunes it'll create a fresh one,

- then dragging songs (importing) into it (I don't consolidate files into iTunes, so the files stay where they are),

- importing playlists (one by one just like with export). 

After a fresh library was built like this, I could see the music and playlists without issues in Garmin Express, even if the songs weren't on "C:\", or like in my case they were also on a completely different SSD then the system one. So Garmin Express does know how to access those files, it just sadly doesn't say anything if it can't read the library properly. 

The downside is losing the ratings and playcounts, but I rather sacrifice this, then not having working music sync. In my case the library was like 7 years old and I'm sure it was somehow incompatible with GE. 

Backup the library and try it out, you can easily just import couple songs to check it out first if this is the case and if the songs will show up in Garmin Express. As long as you have a backup of the "iTunes Library.itl", you can easily restore it back. But if you'll get working iTunes sync with Garmin this way, you won't want it afterwards anyway.

Run iTunes. Go to File > Library > Export Library > Save as 'D:\Users\xxx\Music\iTunes\iTunes Music Library.xml'
xxx is your user name.
Note that I have iTunes on my D: drive.
Then run Garmin Express, selecting iTunes as your source.
At least on my PC iTunes deletes the xml file every time I open iTunes. So you will have to recreate it whenever your iTunes library is modified. In the meantime, Garmin seems to need the xml file every time it runs.