You select an entire volume, Macintosh HD in your case, as your source in SuperDuper!, but it clones only the info in that volume, so when you clone MHD you're cloning only Sierra. If you have two or more volumes you can clone each one individually.
OK. That was semantics for me. I do know how to clone to my Ext. HD. I will erase it and maybe re-clone Sierra.
The words aren't interchangeable. The extensions you've got now are not apps (.ext, I think, suffixes), but beginning with Safari 12, even though the pref pane is still called "Extensions," your old extensions will no longer work, and you'll have to download apps (with .app suffixes) to replace them.
OK. I will download the apps. I didn't know the difference. Thanks.
MacBook Pro - M2, Ventura 13.6 Safari Tech Prev 17.0 Safari 16.6 Firefox 116.0.2 iPhone 7 Version 15.8
