Not seeing your presets in the plugin's folder in your Final Cut Pro libraries?
If you have installed a plugin and the PFS App also shows that the product is installed but you aren't seeing the presets display it may be that you have either text entered or 4K and/or HDR filters applied to the Search Bar for that library.
If you click on the magnifying glass icon in the search bar you can uncheck the filters there and you will see the presets appearing. You will not want to have these filters applied when trying to view and apply the presets from your library browsers.
Please see the images below!
Press the magnifying glass icon in the search bar.
You can click the 4K and/or HDR filters to deactivate them.
You should then see your presets appearing in your library browser.