3Blue1Brown
Media
https://www.youtube.com/@3blue1brown
Overview
Grant Sanderson's mathematics channel, animated with software he wrote for the purpose. The series Essence of Linear Algebra and Essence of Calculus teach the subjects by showing what the operations do to shapes rather than by manipulating symbols, and the later series on neural networks and transformer models does the same for machine learning. Standalone videos take a single problem, from the Fourier transform to why the digits of pi turn up in colliding blocks, and build the answer visually from nothing. He also runs the annual Summer of Math Exposition to encourage other people to do the same.
Notes
The best explanation of almost everything it covers, because it shows rather than tells, and a demonstration that difficulty in mathematics is mostly a failure of presentation. The neural network series is the clearest account I know of what a model is actually doing when it "learns", which is background to my position on Substrate Independence: once you have watched the computation, the question of what it is made of looks less important. Also simply beautiful, which is not a requirement, but helps.