I do not think you can control video or focusing on a remote screen.
Forgive me asking for clarification but have you actually tried it with a 6D MK2? The reason I ask is you say you 'think' it doesn't work but I need to know for sure one way or the other.
Tne 6D MK2 makes a lot of sense to me as I already have a lot of Canon gear, but if I can't control the video when the camera is out of reach then I will have to look elsewhere.
Why trust a bunch of dogs on the internet? Rent one and find out for yourself.
Don’t bother wasting your time with a rental. Save your money. Touch screen focusing only works with the local LCD screen. End of story. You cannot control video with the EOS Utility across Wi-Fi, either. Using a USB cable won’t fix it, either.
The EOS Utility is designed for remotely triggering the shutter for capturing stills, not video. There is no accommodation in the EOS Utility for “pushing” the video record start/stop button. None. The EOS Utility cannot do video, not at all.
I wonder if maybe it varies depending on which country?
There's a guy on an English forum that says it works, and there's this German video
where at 9.44 there's certainly a Rec Start button but unfortunately I don't speak German to know what is being said.
Unfortunately there is no rental company accessible to me that rents the 6DMK2
The devil is in the details.
I do not need to speak German to notice that she is using a smart phone, not a tablet. She does not appear to be using the EOS Utility, either. You asked about using a tablet and the EOS Utility over Wi-Fi. What was the English guy using?
If you stop and think about it, really think about it, you will quickly realize why the EOS Utility is not supported in video mode. In order to put the camera into Video Mode, you must turn a switch or knob on the camera. This cannot be done remotely via USB or Wi-Fi.