It actually is not one of the branded hardware, is another model in which I installed Manjaro, but I consider is an interesting problem.
Last program installed was Tuxedo Control Center, from Official Repos. After one day and probably overnight sleep (I tend not to turn off my computers) I could not wake it up. In this particular model you have to press the On/Off switch to do this.
After a Ctl+Alt+Del and seeing flashing the KDE login screen, a dark (like off) screen again. If I close the lid, on opening again I can see the flashing the KDE login screen.
Boot again and conjure the Grub screen and select another kernel, but same behaviour on each one of them (5.18, 17 or 15). The BIOS screen shows perfectly and there was no change before or after, so I suppose is not an hardware problem. I tried to login to a console and then SSH from another computer, I tried to login in the black screen but none of that worked.
Next I bring it to my desk and and start looking in this Forum and in Tuxedo web site for problems similar to this, but nothing pops up. But what pops up is said laptop suddenly shows the login screen. I login promptly and went to check which was last program updater or installed, and it was “Tuxedo Control Centre” so I blamed it for this scare.
I uninstalled it and everything works wonderfully like before, so I wanted to let know the fine folks that use Manjaro to be aware of the potential problem.