https://forums.adobe.com/thread/2548795
When the Maintain Aspect Ratio box is unchecked, Free Transform should be non-proportional.
However, in version 20 (Oct 2018 release) the aspect ratio remains locked whether or not the Maintain Aspect Ratio box is clicked. Only using the shift key (new behaviour) seems to work.
Reported in Adobe Photoshop forums by Win 10 users.