Thanks a lot for that link! I know nothing of Apple stuff and a friend has got an old iMac that he thought was unupdatable but it seems there's a way. Cheers!
It advertises itself as midweight, so of course you can find lighter distros/DEs out there, but the snappiest desktop Linux I've used recently is MX Linux, with comes with a very polished Xfce... Try it, it has a lot of pro-user features!
I guess you're alluding to DockbarX [1] and xfce4-dockbarx-plugin [2]. Those, and specific dock apps (there are quite a few) are the alternatives as of today.