installing on PC, I'm opening the .aex with after effects, like clicking on it, when it gives me the error. I also tried like the script installer, and placing it directly in the directory but it still doesn't show in the windows section
To install native plugins like PixDither, you have to put the .aex file into the correct directory:
C:\Program Files\Adobe\Adobe After Effects (version)\Support Files\Plug-ins
In my case, this is: C:\Program Files\Adobe\Adobe After Effects 2022\Support Files\Plug-ins
and then it will show up under the "Wunk Effects" category in the effects panel. Simply clicking on the .aex file will fail as it is not a file that can be trivially opened or installed as a script.