Safari App Extensions are less capable in various ways than Safari Extensions, and many currently available and widely used JS extensions cannot be converted to

Safari App Extensions are less capable in various ways than Safari Extensions, and many currently available and widely used JS extensions cannot be converted to them. As an example: uBlock Origin is a Safari Extension that simply could not function as an App Extension due to lack of APIs. It is present in the Safari Extensions Gallery, which is deprecated in Safari 12. However, the current version of uBlock Origin is broken. The only fix at this time is to install an older, developer-signed release from the homepage, which is physically impossible in Safari 12.