Does that matter all that much? Not necessarily, but it's good to know things like whether or not your regex can blow in time complexity due to back tracking or not.
Other than that, there's a syntax overview that's very strong, and the rest is pretty straight forward from there - just applying sequential pieces one after the other to build your pattern.
I also like those regex crosswords - those are some of my favorite puzzles to do. I wish there were more of them! https://regexcrossword.com/
If something gets too complex, I tend to write a Tokenizer / Lexer these days. It's not that hard.
You can enter something like this in ChatGPT: "Please give me 5 regular expressions that programmers find most useful."