Do you like math :D ? You can calculate the position using the angle of the camera...
or there is already some inbuilt expressions for this:
https://www.construct.net/en/make-games/manuals/construct-3/plugin-reference/3d-camera
CanvasToLayerX(layer, x, y, layerZ)
CanvasToLayerY(layer, x, y, layerZ)
Transform a position in canvas co-ordinates to layer co-ordinates on a Z plane given by layerZ. This is similar to the system expressions of the same name, but working in 3D.
LayerToCanvasX(layer, x, y, z)
LayerToCanvasY(layer, x, y, z)
Transform a position in 3D layer co-ordinates to 2D canvas co-ordinates. This is similar to the system expressions of the same name, but working in 3D.
I don't understand what this expression returns. It's just other numbers that also don't match the cursor position in 3D space.
Okay, in my project I'll try to use all planes with z = 0 and Mouse.x("Layer 1"). Then the created object gets the correct position.
Maybe in the future I'll figure it out, but for now it's very difficult.