The adblocker only pass a content blocker (a set of rules, https://developer.apple.com/documentation/safariservices/creating_a_content_blocker ) to Safari, so it doesn't need any permission.
Anything else will require permission.
Does your extension have any content scripts or style sheets? If it does, then Safari will say the extension has permission to read the DOM. If you remove the content scripts and style sheets, then Safari will say that the extension
And for that error you were seeing - try doing a clean build of your extension. That should help.