What’s wrong with them?
I just watched the type punning video right now but multiple statements he makes are wrong e.g. "us being able to say: I am treating this memory I have than as a different type than it actually is. And you can see we can do that really freely."
C++ has strict aliasing rules, hence type punning as he describes it is not possible. Furthermore there is no way to guarantee that a struct does not contain any padding. (yes compiler extensions exist to support it, that's however not part of ISO C++).
In my opinion this a serious concern, since especially new people trying learn will get these wrong habits and once learned it's hard to get rid of them.
Instead I would recommend reading a book, written by people who really have a deep understanding of the language.
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looked into the Union Video, undefined behavior again...
While I have seen worse, I would still not recommend these