[Vetch]

It's difficult to find material that's a series, rigorously demonstrated and advanced at the same time (there's lots excellent material that ticks either one or the other of those boxes). Here are some examples I subscribe to that come close:

Covers Quantum Field Theory and General relativity in as approachable a manner as I imagine is possible while still going deep into detail: https://www.youtube.com/c/viascience/videos

Theoretical machine learning, Information theory and probabilistic inference: https://www.youtube.com/user/mathematicalmonk/videos

Heavy emphasis on analysis and measure theory: https://www.youtube.com/c/brightsideofmaths/videos

While ScienceClic's coverage of differential geometry topics is mostly a thin vertical slice of the subject, it covers it with incredible visualizations and pedagogical approach: https://www.youtube.com/watch?v=xodtfM1r9FA&list=PLu7cY2CPiR....