Safari App Extensions are packaged within a container application. In the case of this Reload Button extension, the containing application does nothing, but you must launch it at least once to let Safari know that the extension exists. After the first launch, you never have to run the application again—but you do need to keep it installed because the extension lives within the application.
If you’re running macOS Big Sur or later, try this version:
The legacy version of the Safari Reload Button extension works in Safari 11 and earlier.