When creating a tangent curve the user can add a radius to the curve but cannot press the "D" key to enter a length of the curve. This feature is available in the Desktop version.
Yes it will be added sometime in the future.
Where are you using the D key in ArcMap to specify the arc length for a tangent curve?
Its actually not the "D" key in the desktop because "distance" in Pro is "length" in desktop. When creating features and wanting to add length or distance you can also right click to get these options. The "D" key is the shortcut.
Retrieving data ...