generally, book moves are just some common opening moves, but after around like 3 or 4, chess.com stops them, even if theory goes for way longer, also some variations of theory stockfish doesn't like, but if you learnt from a youtube video or trusted source, it still might work
Book moves average

wait, do you mean like 7 moves like 1st move white second move black, or like 1st move white, than black, 2nd move white, then black, and so on?

oh, I never got 7 book moves, as even if I follow theory, it does count as a book move, but just says best move

Here, this is extremely random game I don't even know who they are but check out the first like 10 moves by each is a book move. https://www.chess.com/analysis/game/live/128591544083?tab=review&move=20

Don't worry about your number of book moves. More is not better, as by definition book moves are ones which have been explored and are considered "previously explored" for both sides. You can play 0 or 20, but the real thing you need to worry about is that your first move once you leave the book is not a serious mistake. If it is, you don't know the opening well enough and you should either learn it better or switch to a simpler opening. If anything, if at your level you're playing tons of book moves, you're probably spending more time learning an advanced opening than you need to be.
If your opponent is consistently leaving book with a mistake, then you are good enough at the opening and should study something else. And at your level, opponent will quite often leave the book because they don't know the openings well. By definition, though, if your opponent leaves book, you are also out of book. So again, more book moves might just mean your opponents are getting stronger and have more knowledge.
For reference, in blitz I leave book after an average of 3 moves. And I'm over twice your rating.
I'm a beginner, picked up chess less than a year ago. I reached 720 elo, I know that isn't very impressive but I was wondering about book moves. I checked my insights and I average 3.4 book moves white and black. Where should book moves average be for my 720 elo?