With MATE, screenshots are saved by default on the Desktop, in contrast with Cinnamon and Xfce, which default to ~/Pictures. Consistency would be nice here.
Testing Touch on MATE as requested -- actually this seems better in both regards!
On same system -- Touch works seemingly flawlessly, better than either Cinnamon or XFCE images, I wonder what that tells us...
window list - no preview when the window is minimized, previews get orphaned when closing a window using middle-click in the window list. If it's the last window being closed, the preview stays forever., otherwise it goes away when another window list item gets hovered.
The input/output icons are part of a menu item, they're not an indicator, I considered them an action.
window list: icon not hidpi
panel: separators black, doesn't fit theme
laptop panel: shows muted mic and output icons