Hello @sguyader
Thanks a lot for your update on this topic!
In the recent past, I have taken a look at the documentation concerning the Local adjustements.
On the one hand, It is quite technical, which is good of course! On the other hand, It is also a bit intimidating for a newbie (IMHO).
Unfortunately, there a only a few video tutorials concerning Rawtherapee on YouTube and none currently regarding these new Local adjustements tools (for Darktable there are plenty of video tutorials and I suppose this is one of the reasons of its popularity).
Lately, on YouTube, I have kindly even asked whether it was possible to get a video tutorial on this topic but the French creator of that channel [1] replied that he had the same problems with the documentantion and it was unable at the moment to record a video tutorial to be posted on his channel 
I have recorded many video tutorials myself (with Obs recorder [2] and edited them with Shotcut) but they are related to Sqlite stuff. With Rawtherapee I am a beginner
[1] https://www.youtube.com/channel/UCbwyZ6cUTNC6PWBSqud5VdA/videos
[2] https://obsproject.com/