Actually, this must be a bug. I tested it against upstream vanilla GNOME icons, and for some reason Solus' Adwaita icons are not 3.32 like they should be. GNOME 3.32 released a new set of 2D icons, and while Solus is showing version 3.32, its Adwaita icons are <3.30 (i.e. the old 3D icons). You can just check this against any 3.32 screenshot. Nautilus is an obvious one, but really most of the Solus "3.32" Adwaita icons are not 3.32. This shouldn't be the case. I'm not sure if there was an overwrite, a renaming error, or what. I tried rebuilding the Solus icon cache to see if it was an update issue -- no go. Also extracted Solus Adwaita 3.32 icon theme eopkg, and they are definitely not 3.32.
I would never not use Papirus or Numix Square/Circle because I care about beauty in my UI life, but the fact remains this is definitely a versioning bug of some kind.