I'm currently having the same problem with the KoboTouchExtended plugin:
https://www.mobileread.com/forums/sh...d.php?t=211135
About two weeks ago, there was an update to 3.5.1 (from 3.4.4, which is what I have) which my system never picked up. Yesterday, an update to 3.5.2 was posted and it's still not showing in Calibre. I've filtered my Plugins by All, Installed, and Update Available with the same result. Interestingly, Calibre notified me of today's Kobo Utilities update to v 2.14.1.