Can we please use mdi:window-open-variant and window-closed-variant as standard the standard one has bothered me from day one!
you can customize them to use those icons
Do we use variants anywhere else? We should probably keep this standardized
The non-variant icon is USA style window that open/close with a vertical movement.
This type of window is probably used in some other countries but I don’t think it is the more common worldwide so probably less representative of what HA user can have at home.
Also, the design of the icon make it difficult to distinguish open/closed state like stated by OP whereas the variant icon is well more explicit.
Linked to this is that there is no easy way to customize state related icons (see this feature request).