The contents are rendered through gtk/cairo which not only goes through https://www.xquartz.org/ but also doesn't use GPU rendering (it was experimental 3 years ago, maybe better now). The main issue seems to be that neither Inkscape nor gtk people have low level Darwin experts or time available to invest in debugging the whole rendering stack. See for example https://gitlab.com/inkscape/inkscape/-/issues/1614 and all the other referenced issues for all the gory details.
This is very insightful, thank you. This might make me switch back to wxWidgets in fact. Desktop GUI is new to me and I have been trying electronjs(too fat), wxwidgets, gtk, flutter, maybe even Kotlin, looks like I will stick to wxWidgets.
"Qt has better support on MacOS(but GTK4 is doing well with MacOS nowadays), and the team uses Qt for another product so it makes sense to do audacity in Qt as well"
How does wxw and gtk roughly compare? I have liked the UI of Audacity moderately more than Inkscape, but I don't know where framework versus implementation is at play.
wxWidgets uses whatever GUI functionality is native for each OS instead of implementing its own (though there is also a wxUniversal backend which does its own controls but i'm not sure how complete it is). On Linux wxWidgets can use Gtk, Qt or Motif (though Motif doesn't seem to be tested much and while it does compile and work, there are a bunch of bugs).
I was with wxwidgets now switching to gtk, as the latter is way more widely used, wxwidgets is native looking for each OS, gtk has its own appearance, both shall do fine.