USB accessories disabled when connecting external display

As usual, even after a lot of tweaking and searching, I find the solution right after asking for help online... :)

It seems that going to the display menu and disabling the DDC/CI function (in "System Input", then "OSD Setup") did fix the issue. If I understand correctly, the DDC/CI is a protocol that enables the computer to directly control the display setup like brightness, contrast and other things. Apparently, it doesn't please the Mac USB-C connector...

I'll keep this thread updated if I encounter another problem with this particular issue. In the meantime, I hope it can help other people in the same situation.

Ok, new issue: if I power off the display (using the built-in power switch), the Mac says again the "USB accessories" message... The only solution here is to plug out the display and plug it in again, but this is not a reasonable solution...

And even then, if I put the display to sleep mode, there is absolutely no way to waking it up without plugging it out...

I suspect it still has to do with the ability to control the display from the computer: in a normal situation, the display can be powered on or woken up by the computer. And here, something doesn't like this ability...