What does "this is your last book move" mean in the analysis report?

For sure!

Look out!!!!! Sometimes book moves can be blunders! 📖👎

"This is your last book move" in an analysis report typically means that the decision or action being described is your final opportunity or move in a particular context.

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Hey, does "this is your last book move" means that this was last book move performed by me or my opponent (there are more book moves) or this is actually the last book move from the theory? 

It is saying "Your move" or "your opponents" move.

A player of IM level, and higher, is likely to get a " last book" move at 10-15 moves into some openings.

Magnus, and those close to him, will be able to recite/play 20-25 moves into almost any opening, before veering into non book.

Thank you! What is considered the good average number of book moves per game?

It means nothing, since the book which game review uses is inaccurate. It includes silly lines and fails to include highly theoretical lines.

Siuuuu CR7

"Book moves" generally have some theory behind them. They may not be the best moves available but they tend to at least be adequate.