For Preference, the folder is named “preference”, so when you install the child theme for that, it looks for the parent theme which is the “preference’ folder. So this one should be working, or is it still not finding it?
There is a difference with the free and pro version, so you want to make sure that the child theme for Preference (not the Lite version) is installed if you install (or installed) the child theme for that one. If you are using the Preference Lite theme, then the child theme for that will look for “preference-lite”. The child theme for Preference Lite is found in the theme files in a folder named “child-theme”.