First of all, thank you for your support :). Let me answer you questions:
I assume that original sample means jpg Out Of the Camera.
Nope, sorry, I should’ve been explicit about that. That’s a screenshot from the working image on RawTherapee. Screenshooting generates a PNG, which doesn’t have the desaturation problem. Then, the file was converted to JPEG.
rawpedia is your friend
Yep, I’ve read the Eek! page, and two related to Color Management (https://rawpedia.rawtherapee.com/Color_Management and https://rawpedia.rawtherapee.com/Color_Management_addon). There I realized that I hadn’t chosen the output profile (coming from Lightroom, I had expected it to be an export step). Anyway, selecting sRGB didn’t make a difference.
Very saturated colors do not fit into the srgb color space and cannot be displayed on normal screens.
Yep, but that’s not my case. The first image is a PNG screenshot of what I’m seeing at RT, which is later converted to JPEG and still looks fine (maybe some subtle nuances, but you need a trained eye for realizing). That proofs that the colors of my image fit into the sRGB space.
It is also possible that it is a combination of the two factors.
Nop, I tried with maximum quality, no difference.
What kind of screen do you have and how have you calibrated it?
A Dell U2713H (IPS panel) that I calibrated with a Spyder calibrator years ago. But my laptop (XPS 7590, uncalibrated IPS screen) shows the same colors. Anyway, because of the PNG -> JPEG conversion results, I wouldn’t say that it’s the problem.