It appears that my plug-ins I created for GIMP 2.10.38 and Python 2.7 are still being downloaded, so I offer another two should they be of interest to anyone.
The first is eq_sat_mask_h_m_s.py. This creates 10 independent masked layers of different saturation (with a small overlap at the transition between layers to enable their blending).



This generally has proved to be overkill, so I created saturation_h_m_l.py. This gives 3 masked layers which are of high, medium and low saturation.



With these plug-ins, once the masked layers have been created, the possible adjustments within the layers are not restricted to saturation - any of the available controls can be used.
The same is true for the luminosity mask plug-ins