Fletcher on 27 May, 2020 12:23 AM
If you go to Preferences ->Appearance, there is a button that takes you straight to the themes folder. Any themes you put there can be used.
As for images -- Composer needs permission to read files you didn't open, and asks for permission when you open a file that includes images. Did you give it permission to open the requested folder? Close and reopen the file to trigger it to ask you again if necessary.