Ok, I tried with a different screen and different HDMI cable, and I still see a flickering in the screen. This does not happen if I use the HDMI directly in the HDMI port on the laptop. It is not the adapter either, I borrowed a different USB-C to HDMI adapter from a friend, and the same happened. I'm using the patch for 306 as 105.
I tried with other patches, none worked, I can only get video using 306 as 105. I don't know how to enable 306 with my ig-platform-id if that's needed. In ioreg I can see the external screen connected to 105, and it appears as a 04 port type (not HDMI). That is correct I presume.
A thing I can see is that I don't have any option to mirror or extend using the USB-C video output. Is this correct? With HDMI I can see the external screen in screen settings, and I can choose to mirror or extend. With the USB-C as it is now, I can't do that, I only get extend screen if the laptop's lid is open (internal screen is active), or use it as the internal if the laptop's lid is closed.
EDIT: Problem reporting files attached
EDIT 2: If I let the screen go to sleep by not touching anything for more than 10 mins, when I wake up the screen, the flickering is much worse, and it remains badly flickering until I go to the screen settings, and change for example 60Hz to 50Hz. After that, the flickering return to normal. It flickers, but not so much as after waking the screen. The difference is really noticeable. Then I can set it 60Hz again and no problem. But again, if I let the screen go off, when I touch a key on the keyboard or mouse to turn on the screen, the flickering is noticeably worse again.