IMHO: in order to say yes you are usually saying at least one or more no's. Otherwise the lack of those other no's will eat you alive.

Oddly enough, though, all those things you listed are possible if you reduce the scope and scale of the projects. Its a matter of saying no to massive undertakings and be pragmatic about it.

A "programming language" doesn't have to compete with C or rust or something equally huge. It could be a little DSL instead. "Cryptography" could be a key store or other simple encryption tool. The "sci-fi epic" could be a novella or even a short story.

But at the same time, even those undertakings might still be too large a bite to take out of your weeks.

So, as you say, prioritise and accept your own limitations.