Beyond videos, another great medium for learning about past FRC robot design is
the whitepapers and engineering notebooks made available by many teams.
You may find that an understanding of how an FRC robot works is often best gleaned from reading about those from top teams.
1114 makes its robot display boards, engineering notebooks, and CAD models available; likewise for
254; and
971; etc.
As far as videos go, VexPro's
BuildBlitz documentation is a good start.