Connecting Samsung Galaxy Tab S6 to HDMI without activating Dex
It seems that it depends more on the TV than on the tablet itself.
In my particular case, I had to select the specific input source in the TV, and only then the tablet sends the image without trying to run in Dex mode.

To summarize, I had these connection methods:


Google Chromecast Ultra: relatively low latency, but very bad quality image for anything not being Netflix or Youtube.
Google/Samsung Smart View: it sends the image via bluetooth, with higher quality than what we have in Chromecast Ultra, but with much higher latency. Unacceptable for videogames.
USB-C -> HDMI "out of the box": The Dex mode takes control, leading to unstable applications.
USB-C -> HDMI, but controlling the input source from the TV: What I wanted.


I hope this might be useful for someone else.
Best regards.