As many have noted, Endnote 20 is a disaster. In Windows 10, when I went to uninstalled 20, I noticed that endnote X9 was still shown as installed (not surprising, 20 didn’t even do a proper uninstall of the previous version). After uninstalling 20, you can right clicking on EndNote X9, and select repair, which then basically reinstalls the program.
What a relief not to have to deal with version 20. Also, 10 comes after 9, not 20.