Hi there! I’ve been doing some testing on my own end, and I can get the Mouse XY 2D-Axis Input Mapping Context to translate to an Axis 2D (Vector 2D) Input Action without holding the mouse button down if and only if Show Mouse Cursor in the Player Controller is OFF. For some reason, when bShowMouseCursor is true, it seems to block automatically registering the mouse into the game window. You have to hold down a mouse button when this is true.
I believe that, under the hood, this boolean is giving the same behaviour as the default “Shift+F1 to detach mouse” functionality when the game window does capture the mouse i.e. it’s not just showing the cursor like it suggests, but actively de-registering it from the game window so it’s essentially not-interacting with your game until you click into the window. If this is true, the boolean is a bit of a misnomer.
Not sure if that is the problem you were running into? Feels like buggy behaviour to me.