iPhone X or Canon 77D - which will produce better quality?
Well, this hardly depends on what you want to do and need.
If you simply want to create cinematic images, 77D will be a lot better because of the bigger sensor.

If you need highly technical and sharp images, like I would expect it from a tech YT channel, I would take the iPhone X.

In the end, it matters more how you handle the camera, than what it can.
Espacially lighting will make a huge difference on both cameras.

So facts are, iPhone X video will look cleaner, but 77D will be more easily to achieve cinematic footage and give character to the image