As my favourite Saul Goode luminosity mask script is not working, owing to a bug in GIMP 2.10.14, I looked for an alternative.
Tin Tran's script works well, but it is not possible to make changes cumulatively to the various layers. So I decided to modify it (knowing nothing about Scheme!). Fortunately Tim's script was very well commented.

I think I may have succeeded. I hope others will test this, comment and criticise.

A quick example of the possibilities I hope it will create (with apologies to dinasset for spoiling yet another of his excellent photographs).
I created a layer group with L and added a blue overlay layer. A layer group of DDD, I added a yellow overlay layer.

david.

Edit: I discovered an error in the script - now updated.

David, did you try also "python-fu-setup_luminosity_masking_layers" by "Kevin Thornton"?
Just in case you do not find it:

dinasset,
Thanks for the link.
It is a good alternative to the Saul Goode script.
My new script (the modification of Tin Tran) creates seven masked regions of brightness, all different, which can be used separately or together. At least that is the idea!
david.

Yet another error discovered!
Masks LL, LLL, DD, and DDD behave as I intended, but at present I am unable to persuade the script to subtract DD & DDD from D - the equivalent problem for the L mask and I cannot get all the Lights & Darks to subtract from the M. So, at present L, M & D remain as the previous version.
david.

On gimp 2.8 I used the medium setting in the mask layer but ticked the box which reverses it

I then followed the gimp contrast mask legacy tutorial, I've not done enough posts to link to it, on a layer with a copied background image and the layer mask mentioned above and it seemed to work quite well

the image retained quite a bit of punch but a lot of detail was restored and I assume the dynamic range increased

I use soft light or overlay mode on the layers, maybe there would be a better way of doing it, I understand in GIMP 2.8 they are quite similar

There is also my own "ofn-luminosity-masks".

IMHO:

- The masks used in Patdavid's tutorials are OK because they can easily be constructed by hand, this doesn't mean they are the best solution in a script.
- A much more flexible way to construct a mask is to apply Curves to a channel that contains the layer luminosity
- There is no point in a script to build all the masks. As soon as you make changes, the mask is no longer valid. If you use a "Darks" mask to make changes, pixels in the midtones will change, and if you then want to change the lights, you should redo a "Lights" mask to take these changes in account.

I get the impression how good these techniques in general are though by the number of versions people have done, I noticed some other interesting scripts when I looked for the ofn luminosity mask

I look forward to also trying the stipple and other similar scripts that were there I did take part in the halftoning from grayscale image conversation which touched on this, if I have understood the function of them right: it will be a while before I have the time to have a go