Previously I have suggested that the defringe module should not be depreciated because there are some images where it offers the best solution to chromatic aberrations. The attached image is one example I recently stumbled upon. I have included the xmp file which includes the defringe module being activated.
Tank.ORF.xmp (15.2 KB)
Tank.ORF (11.5 MB)
Wrecks the flag 
Adjustment could and should be localized with a drawn mask.
@dtrtuser the very large chromatic aberration tick box made all the difference with this image. Thanks for pointing this out. Also at first while lens correction helps with the TCA it introduces distortion correction, However, because the lens correction module is well designed I see I can select TCA only. Your proposed solution works well and I am happy to have egg on my face. 
EDIT: I would add that localizing the adjustment with a drawn mask is needed to avoid issues with the flags that @priort pointed out.
The details mask is good to help with this… I too got about the same result and sometimes I can get even better with an instance of CC module and using the gray tab set to 1 for blue and then drop the opacity to where it works and of course you need to mask it…
Deprecated just means not shown. Its still there, make a preset, its not being removed. You can still use it.
The trouble with that hard deprecation is that someone who has never used a module cannot create a style by copying it from an image, and even us long-time users would have to hunt quite a bit to find an image that has the module enabled (I only keep the image sets I actually work on imported into darktable, so searching would have to rely on greping the sidecars). I understand that they are deprecated for a reason, but they still need to be maintained for backwards compatibility (being able to edit old images), so I don’t know how much work is actually saved.
I often wonder this myself. But I trust in the developers to know what is best since it is their time not mine being taken up to maintain deprecated modules. However, I did find the defringe module useful with some images and was sad to see it get depreciated. Thanks to this forum I am shown some alternative paths to solving the fringing issue from this Olympus TG6 image shot in Saigon.
I tried this with defaults for sigmoid/scene-referred.
Added raw chromatic aberration and disabled chromatic in the lens module. Looked pretty good immediately.
Check the branches:
Not even defringe fixes that without destroying the colour in the flag. Masking may help, of course.
I think the severely blown sky makes this even worse – and it’s not only CA, but a mixture of artefacts.
Yes. You are fully correct with your idea about the blown background VS branches.
Reviewing @rawfiner 's video again I noted one strategy on severe CA was to use two instances… one using lighten only and one darken only. I tried that and didn’t see a huge improvement but using 2 instances set to darken wasn’t too bad. And using his approach to maximize the strength to help find the right radius and then back it down to preserve color artifacts helps to dial it in as well.
I think depreciation is more aimed at the fact that the #1 criticism of darktable is “omg too many modules and too many ways to do things.”
Is this not the beauty of DT. You are not dictated to but given choice. Yes I understand it can be all overwhelming for beginners who are not receiving guidance. However the developers have put together a module list for beginners.
Oh I agree, but if you hear it enough then at some point you have to listen (?)
I’ve heard it enough (though it doesn’t bother me), but I’m also not a dev.
I am teaching a DT class at the moment. The first thing I did was go into preferences and set up the Sigmoid option instead of filmic. I then used the manage module layouts options to only show the modules I needed the students to see.
Maybe the developers could make DT easier for beginners by making Sigmoid instead of filmic the default and having their beginners module as the default for a first time installation of DT. Experience users would know how to set up the module layout to their preference whereas a newbie may not find the beginners layout module for themselves.
You can certainly open a feature request, but I’d expect it to be met with quite a bit of push back.
Frankly I use 3 sliders with filmic 99% of the time: contrast, white relative, and black relative. That’s one more slider more than filmic.
DT provides a lot of choice and the tonemapper is a fine place to start discussing chocie and trade offs in image development 
