Please ensure you have updated to Astute Manager v2 before proceeding. An easy way to tell the difference is that v2 operates in a larger window, whilst v1 was constrained to a smaller, vertical window locked to the top right of the screen.
With the introduction of the Astute Manager v2, every time you load the application, it will automatically detect and add any new major versions of Adobe Illustrator (eg. CC2018, CC2019, 2020.2+). Therefore, a quick approach to adding a new version of Illustrator to the Astute Manager so that it offers management of plugins for this version, is to quit and restart the application.
Alternatively, click on the Settings cogwheel icon, top-right of the Astute Manager window:
In the Settings page, scroll down to the bottom and click on the Detect Installed Adobe Illustrator Versions button:
All versions installed on your computer should now have its associated plugin folder location listed above.
If all appears to be correct, click the Save button.
When returning to the main Plugins page (top left menu), you will now be able to target the newly detected version of Illustrator for plugin installations and updates: