@Pascal_Obry
It certainly seems to be the never ending story 
I think…
taking the time to read this section:
https://docs.darktable.org/usermanual/development/en/overview/workflow/process/
and this one
https://docs.darktable.org/usermanual/development/en/special-topics/color-pipeline/
in the manual give some good starting tips and direction for new folks… Maybe some suggestions by new users after reading some of these sections for what information was found to be lacking in the eyes of a “new” user would be helpful as that is harder for an experienced person to sometimes pick up on…
Of course there is always room for improvement in any project but DT by its nature and by design in many instances is to expose as much of the editing process as possible. This will not always jive with a simple interface. As well, there will always be a spectrum of users and given the nature, nuance and intricacy of the DT pipeline its not a trivial thing to understand.
@martinus many of the recent tools were introduced and propagated by a dev that went on a color science crusade… just a sample of the context and framework for DT’s inner color workings…and this sort of depth and detail was carried over to several other key modules…
Without a bit of history and a deep dive its hard to just land in to DT and get context for why things are the way they are…it takes time for sure.
Once I started to follow the developement a bit on Github I was much better able to understand why things were the way they were and what suggestions/requests were currently out there along with which ones were being worked on… I know right out of the gate that all of this is beyond what some people are looking for to just “develop” there photo’s but this is the nature of DT and why it actually appeals to many people so its a circular argument in many cases because people come in with another frame of reference…
Case in point for me during the pandemic I had lots of extra time and I was on my computer and I thought I would organize years of photo’s. I didn’t know what raw file really was. I have owned a series of compact camera that captured jpg. I had 15 years worth of vacation and family photos. I stumbled on to rawtherapee and got a bit overwhelmed just trying to fix up my jpg images. I then found DT but back in 2018 I really struggled with the interface. I was lucky enough that a great chap @Bruce_Williams made an epic series of videos that got me past the UI hurdles and the basics of using the program…from there I learned about raw captures and I just spent a lot of time and followed the development odf DT which was massive for a few years with new features and modules appearing and being modifed in rapid succession, and it was only through participation that I was able to hang in there…
Where has this left me…Well I have Affinity photo, Gimp etc etc. I one time bought ON1 photo raw when it was like 40 bucks as was Affinity photo. ON1 has some fancy tools and the UI is pretty good but you know what, I get in to it and begin editing and then I just miss the access to all the tools and presets that I have learned to use in DT. It has taken time but I have a way of working that I am locked into…don’t get me wrong I experiment a lot and will also work in RT and ART because interesting things go on there. However, when presented with the more modern choice with fancy AI selection masking and tone adjustment I still come back to DT…
If I was a pro photographer or had other needs maybe my decision would be different … I can’t say.
Anyway its some random comments… @martinus If you can find a way to immerse yourself you will find that you can get some nice edits pretty quickly and if not the only cost to you is your time so that’s a bonus…I wish you luck and I hope you will have your ah ha moment…