This question was posted on the math subreddit a few days ago and got a bunch of responses, the most popular of which are already here but a whole bunch that aren't:
The French version of the above channel has a lot more videos but unfortunately aren't translated to English yet.
Proper lectures by professors of various math/physics topics unfortunately are scattered around YouTube and I'm surprised no one has gathered a big list of them given that during COVID a lot of stuff has been put online. I've only found the following two channels which gather various lectures given however at a graduate/research level so you're unlikely to learn much unless you have a significant background:
https://old.reddit.com/r/math/comments/w1zyn8/favourite_math...
Of those listed there I would like to highlight this one:
https://www.youtube.com/c/Aleph0/videos
A few others that I've found recently also in math/physics:
https://www.youtube.com/c/PhysicsExplainedVideos/videos
https://www.youtube.com/c/SimulatingPhysics/videos
https://www.youtube.com/channel/UC3L8AcX1xJEhTofnCF2MAaQ/vid...
https://www.youtube.com/c/ScienceClicEN/videos
The French version of the above channel has a lot more videos but unfortunately aren't translated to English yet.
Proper lectures by professors of various math/physics topics unfortunately are scattered around YouTube and I'm surprised no one has gathered a big list of them given that during COVID a lot of stuff has been put online. I've only found the following two channels which gather various lectures given however at a graduate/research level so you're unlikely to learn much unless you have a significant background:
https://www.youtube.com/c/GraduateMathematics/videos
https://www.youtube.com/c/GraduatePhysics/videos