I followed the walkthrough here: https://developer.apple.com/documentation/safariservices/safari_app_extensions/building_a_safari_app_extension?language=objc
and created new target for a Safari App Extension, but it doesn't show up in Safari. The extension should be code-signed, but I've tried allowing unsigned extensions, and it doesn't help.
The "Troubleshooting Your Safari App Extension" article suggests that you can verify your extension is visible to Safari by runnin ghtis terminal command:
pluginkit -mAvvv -p com.apple.Safari.extension
Since the output is "(no matches)" I'd say mine isn't. Unfortunately the author of the article couldn't be bothered to suggest any reasons why this might be, or what you might be able to do about it. I've tried various combinations of relaunching applications and rebooting my Mac, which is often the fix when Xcode refuses to do something for no good reason, but it's no help in this case.
I also tried changing the "SFSafariWebsiteAccess" level to "All", but I don't think that's relevant since the extension isn't showing up at all.
So what's the magic step that's missing from the walkthrough (and the Xcode template) to produce an extension that actually appears in Safari?