I feel for you Karim, seems that the thing you didn't understand the most was actually the thing you were lacking the most: A good Scrum Master. To ensure all the things you found wasteful and confusing, are handled, described, taught, and executed properly. If you want to understand Scrum in-depth there's only three things you can do:
1. Read the Scrum guide: https://scrumguides.org/scrum-guide.html
2. Read the "official" Scrum book: https://www.goodreads.com/book/show/19288230-scrum?from_search=true&from_srp=true&qid=CcVDPUf3WQ&rank=1
3. Just do it. 😉 Either apply as a Scrum Master what you learned in these resources. Or look out for a team that does Scrum well and you will see the true potential of it when applied well.

Good luck on your journey. 👍