Great game
There are 2 technical things I want to recommend:
1) When you select a tile, don't set tile's position as mouse position. You can create an offset = get_global_mouse_position() - global_position whenever you start dragging, then on process when you dragging, the position = get_global_mouse_position() - offset. This way, when you click and drag, your tile map will not snap its center into the mouse, which a lot of time is annoying because of the tile is already set in the right place but should be on top
2) When I put 2 tiles on top of each other, I accidently move of them together. If its kinda similar tile, the 2 stuck together forever. The solution is put your root of all tile as Control or anything control related. In its script, set mouse_filter into ignore whenever something else is selected. That way you can only select 1 tile at a time
Otherwise, really high quality game