For users on Catalina, they will need to manually approve the XPL.
Please follow the instructions stated here: https://forums.x-plane.org/index.php?/forums/topic/193236-macxpl-cannot-be-loaded-because-the-developer-cannot-be-verified/&do=findComment&comment=1774578
If still the plugin is not loaded, follow the instructions shown in this post: https://forums.x-plane.org/index.php?/forums/topic/194055-mac-os-x-catalina-and-macxpl-files/&do=findComment&comment=1935328
You can find more general information about this problem here: https://forums.x-plane.org/index.php?/forums/topic/192252-mac-os-catalina-1015-xpl-problems/
← On Mac OSX Catalina, I get the “mac.xpl cannot be loaded because the developer cannot be verified” error
On Mac OSX Catalina, I get the “mac.xpl cannot be loaded because the developer cannot be verified” error