Yeah, I didn’t go the “Creating a Safari web extension” route, rather I went via “Packaging a web extension for Safari”: https://developer.apple.com/documentation/safariservices/pac...

I note that they say the command has changed from the one I used, it’s now:

    xcrun safari-web-extension-packager

My extension has storage/settings, and it works fine. I have edited no Swift code at all.