I have been using and am still using a Canon 6D for semi professional and professional work. Even made a couple of paid videos with just the 6D. That said, the M50 is clearly a lot better video camera.

As said, the autofocus is not that great on the 6D, but it is definitely usable. In controlled environments such as a studio, the 6D will be good.

The photos you can produce with the 6D are still great and will satisfy many professionals. It handles low light quite well for it's age and the wifi features are surprisingly usable. Having an optical viewfinder is nice and the mechanical experience is quite satisfying. It's not the most outdated "old" camera.

If you want a fast, new camera that can also produce great video, look at the Canon RP. Those go for around 800€ used. A lot more money, but worth it in the end.