When Altium Designer designs a PCB, how to open a slot or dig a hole on the board, whether to use the Keep-Out layer or the Mechanical layer, I will answer here today, both of which are used in practice (and Many people use it), but both are not standardized and there are hidden dangers. The correct way to do this is to use the "board cutout" method.
The specific method is to draw the shape that needs to be cut out on any layer, then select all the lines of this shape, and select Tools-->Convert-->Create Board Cutout from Selected Primitives. This completes a real digging and grooving operation, which can be viewed in the 3D preview.
Here it is said that any layer can be drawn with a shape, but the actual situation is slightly different. If it is drawn on the Keep-Out layer, there will be no copper on the edge of the slot after copper pouring. To have copper on the edge of the slot, it is recommended to use the Mechanical 1 layer. Please see attached image for this.