Mathematica , Colab or LaTeX for exam summarys?
If you are trying to learn something, preparing summaries is an excellent way to reinforce your learning. Editing your summaries to improve them is even better. Summarizing your summaries...

The vehicle you use is less important than that you do it. I'd suggest using a tool that you already know, so that the you can concentrate on the subject matter and not fight with the tool. 

On the other hand, if you want your summaries to be maximally useful, export them in a format that others can use without needing additional software. I don't have Mathematica, for example. In many ways PDF is the most portable format (as the name implies). 

Video has its own issues. Some people can't use it effectively. For example, I don't hear well enough to follow the audio track so youtube is closed to me. Video also has the problem that it is harder to find the relevant things you might need to return to, being a stream. 

However, note that these summaries are most useful in deepening the knowledge of the creator, rather than the users, who would be better served creating their own summaries. Not useless, of course, but not a panacea. What you think of as important to put in a summary, others might not, and need other things that you feel are so obvious as not to be needed. It is the dilemma of any textbook writer, of course. 

In my view, one of the best ways to create summaries is on paper, by hand. This forces your brain to work in a different way than it does interacting with a software tool. There is research to support that, actually. My favorite is just a set of index cards, since they are easy to create, rearrange, index, etc. You can also carry them around for a few moments of reinforcing study. When I was an undergraduate the person who ended up as valedictorian always carried a few cards with him for quick review of his coursework. Also carry a few blank cards so that you can makes notes to incorporate. 

I've discussed the idea of the Hipster PDA in other posts here. Note that you need to follow a few links to see detailed info about the concept.