Dell D6000 - Screen Flickering

[AlbanRampon]

Nicola,

Would you have brand and model for the other products you mention?
The HDMI converter and the other dock more precisely.

Alternate Mode is about passing non-USB traffic on a USB-C plug.

I wouldn't say the issue would be general to all 3-head docks. For instance, the Dell D3100 has 3 displays through DisplayLink technologt... and if it works for your displays on the Dell D6000 I would expect it to work on the Dell D3100 as well.
You might also wish to try with another refresh rate on the HDMI: this could be enough to stop the flashing/flickering. This is a bit burried in the settings, let me know if you wish guidance on that (if so, tell me the Windows version so I can find a relevant article).

Kind regards,
Alban