However, I cannot remove it, because when I try to "unpin" it I get an error "Location is not available".

1. Open Folder Options
2. Click the Clear button

An alternative solution is to recreate the folder and/or file that is pinned to Quick access and then unpin the location.

However, I cannot remove it, because when I try to "unpin" it I get an error "Location is not available".

1. Open Folder Options
2. Click the Clear button

An alternative solution is to recreate the folder and/or file that is pinned to Quick access and then unpin the location.

You can also remove the Quick access Shortcuts themselves by doing the following:

1. Navigate to AppData%\Microsoft\Windows\Recent\AutomaticDestinations within File Explorer
2. Delete f01b4d95cf55d32a.automaticDestinations-ms
3. Reboot

Source: [Fix] Quick access Pinned Shortcuts Stuck or Not Working (Windows 10)