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 (Color Management - RawPedia and Color Management addon - RawPedia). 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.