I've been meaning to reply to this for a little while but just haven't got around to it.
This only really addresses the square/squircle etc. icons as I'm not a fan of the notebook style ones, not that I don't think they look great but the majority of my icons that aren't part of the overall system theme are of the same uniform size and shape.
I feel this is a good improvement, not that there seems to much in the way of cohesiveness, most of the mac icons seem a little random, even in regards to Apple's own icons. I rarely ever use macOS so don't have much to add here but I do like it.
These GNOME changes I'm not so sure about if they are part of a generic "Linux" change as opposed to just for GNOME environments from what I can tell.
I use Cinnamon and to be honest, neither the current nor new icons look particularly well suited. The current icon is slightly too big and doesn't quite match (different/no shadow) where the new one is more appropriate in size but is the wrong shape, Cinnamon seems to use something more akin to the macOS squircle (which you can see in the second pic, I've not been able to find the guidelines to Cinnamon icons so far) and your macOS icon actually seems to fit in better than the Linux or new GNOME one.
New GNOME icon on Cinnamon panel (current icon far right):
New macOS icon on Cinnamon panel (current icon far right):
I'm aware that I can always assign or make/modify my own icon but I have a feeling the the updater script for Linux destroys the default menu item each time it runs for an update which means either keeping a duplicate version of the shortcut around just for the new icon or having to modify it each time.