The focus with Tiled 1.2 was generally on improving productivity. It brings improvements to the object tools, introduces multi-layer selection along with multi-tile layer editing, makes it possible to quickly jump between maps in the same world, adds several export options, and includes many smaller changes and fixes.
This is a companion discussion topic for the original entry at https://www.mapeditor.org/2018/09/18/tiled-1-2-0-released.html