A bit late to the party here but I suspect the original issue is the well documented issue with the drawn mask opacity defaulting to zero (or having been accidentally reset to zero). darktable 3.0 masking inconsistencies & bugs - #2 by elstoc.
If your drawn mask has an opacity of zero it will always cancel out any effect of your parametric mask. Alternatives are to ctrl-scroll before placing the shape, which will change the default opacity, or change the setting in darktablerc to set opacity to 1 (while out of darktable)