Doing a full college course is such a time investment and it usually takes a few weeks to start proving the interesting stuff. I find it more fun to look to shorter content for inspiration. I might realize I don't understand the fundamentals of the topic and then seek out a way to study it.
3blue1brown for math (https://www.youtube.com/channel/UCYO_jab_esuFRV4b17AJtAw)
Everyday Astronaut if you are casually interested in rockets (https://www.youtube.com/channel/UC6uKrU_WqJ1R2HMTY3LIx5Q)
Bret Victor (https://www.youtube.com/watch?v=PUv66718DII&list=PLS4RYH2Xfp...) or Rich Hickey (https://www.youtube.com/watch?v=f84n5oFoZBc&list=PLXsqD83He-...) for programming and design.
Doing a full college course is such a time investment and it usually takes a few weeks to start proving the interesting stuff. I find it more fun to look to shorter content for inspiration. I might realize I don't understand the fundamentals of the topic and then seek out a way to study it.