You can add the checkbox like the other widgets in the init method of the BL_UI_Widgets_Operator for example on a dragable panel widget.

I explain how the Python API is used and lso how it is implemented in detail.

The checkbox works by clicking with the mouse but I also implemenetd the Click and Hover selection that you know from the defaul Blender checkboxes that you can use on panels e.g. for Bool-Properties.

Here you can get the Blender UI Widgets Addon for free:
https://github.com/jayanam/bl_ui_widgets

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