It works when the drive is idle and is OS independant so it doesn't matter whether you have Windows, MacOS, Linux or anything else. There is no way to tell it's working. It's entirely internal to the drive and completely independant of the host PC.
I think to make the GC work, you should disable the sleep mode for the Hard Disk. You can do this by going into
system preferences - Select energy saver. Under power adapter TAB you will see a check box against "Put the Hard Disk(s) to Sleep when possible, you will have to untick the check box.
This will help the SSD to do the GC whenever it is idle.
