I had uninstalled Alien Skins plugin to install a newer version of Exposure (bundled) on Photoshop 2020.
Unfortunately, it didn't remove the plugin from Photoshop 2020 'Filters' menu. It's not a big thing but annoys the hell out of me each time i see it there and obviously no longer functioning too.
Eventually, i found a way to remove plugin from "Filters" menu after you have uninstalled the plugin and this was to manually remove it. To do this you need to navigate to the Photoshop plugin directory.
You can do this in your terminal, type:
cd /Library/Application\ Support/Adobe/Plug-Ins/CC/
Your plugin should in be inside the /CC directory. In this case, it was Alien Skins directory. Now you just need to delete it. Another problem pooped up, it also removed the entry in 'Filters' menu for Exposure because this was the new Alien Skins that was also installed into the same directory. But reinstalling Exposure afterwards fixed the issue.