USB 3.2 (and currently USB-C from it) doesn't support the 48GBps that HDMI 2.1 and 32GBps that display port 1.4 call for. USB supports a max of 20 GBps at currently. It's possible you can get more bandwidth using an alternate mode in the connector, but the spec says you can only guarantee up to the 20GBps over those modes currently. This means the higher resolutions and higher bitdepths (10bit, HDR, etc) may not be possible to push over the connector.

This is why Thunderbolt 3 requires special active cables to get the additional bandwidth by amplifying the signal to help get around the bandwidth limitation of the connector in a passive configuration.

That's why usb-c is failing. You simply can't know what that port can do.

Is it power, video, data? Do I need a special cable for it? Nobody knows.

Here's a good discussion about how that has turned out: https://news.ycombinator.com/item?id=15473777

I would favor if monitors, displays, and projectors have both USB-C and Ethernet. At the moment all types of displays still have DVI, DisplayPort, HDMI or even legacy like VGA, SCART.

USB-C and Ethernet are capable of 10+ Gbit speed, and the cables are cheap, not the premium one pays for HDMI 2ab cables. Also Ethernet cables with CAT6+ are found in most buildings. If you want to connect a big screen flat TV dozens meters away or a projector 50 meters away, you need repeater devices and fragile cable arrangements, while with Ethernet cables it would be no problem.