Inkscape slowness on mac was never an XQuartz problem. All GTK (or maybe it's Cairo) apps are just terribly slow on macOS (even scrolling in meld is janky as hell and meld doesn't exactly do very much), and the new Inkscape is no exception. In fact, by some accounts the XQuartz version was if anything better in this regard.

There's a long discussion about it here: https://gitlab.com/inkscape/inkscape/-/issues/1614

@je42: It becomes usable though if you Get Info on the Inkscape application in Finder and then check the "Open in Low Resolution" checkbox.

There was recently a bug related to this on the gtk issue tracker too: https://gitlab.gnome.org/GNOME/gtk/-/issues/3714

I don't think there is going to ever be much interest in getting this fixed in GTK3, but apparently performance has improved in GTK4, which should be hardware accelerated on macOS now: https://blogs.gnome.org/chergert/2020/12/15/gtk-4-got-a-new-...

Thanks !