Ok, it was hard, but I finally entered RCM mode.
Since I use a MacBook, I am using Web Fusee Launcher, and Switch is correctly detected. Once there, I have 2 different payloads to choose from: "SX OS Payload" y "hekate - CTCaer mod v4.0 Payload".
In both cases, output is as follows:
Qequesting access to device..
Connected yo NVIDIA Corp. APX
And that's it, nothing else appears at the web application nor at switch screen.
What am I missing? What about the backup? Should I have made it somehow else, or is it the next step?
Additional data: I'm on firmware 6.1