Being absolutely unable to solve this issue on my PI-4, I decided to roll-up my sleeves and start all over again.
This time, instead of using Astroberry, I started from scratch using the Ubuntu 21.10 desktop.
I installed all the necessary packages (Indi, Ekos, VNC, etc).
Also, I opted for an external drive (in this case an SSD) instead of an SDCARD (Ubunru 20.04 does not allow that but 21.10 does).
This way I have better perfomances and a lot more space on the drive (at least with the material I had in hand).
After installing everything and swearing from time to time I managed to make almost everything work again.
And guess what: my problem dissapeared. Moreover, my colors are now 14 bits as they should have been, instead of only 8 bits as they were in my previous setup.
I cannot tell which of the modifications hit the nail but one of them did.
However, I am now stuck with a problem I didn't have before and that I will talk about in another post.