Video 1.
Yang-Mills 1 by David Metzler (2011)
Source.
A bit disappointing, too high level, with very few nuggests that are not Googleable withing 5 minutes.
Breakdown:
Video 2. Source. 2 hour talk at the Kavli Institute for Theoretical Physics. Too mathematical, 2021 Ciro can't make much out of it.
Video 3.
Lorenzo Sadun on the "Yang-Mills and Mass Gap" Millennium problem
. Source. Unknown year. He almost gets there, he's good. Just needed to be a little bit deeper.

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Yang–Mills theory is a fundamental framework in theoretical physics that describes the behavior of gauge fields. Named after physicists Chen-Ning Yang and Robert Mills, who proposed it in 1954, the theory is a cornerstone of the Standard Model of particle physics, which describes the electromagnetic, weak, and strong forces.