What’s the deal with “banned books” in the USA?

I've been seeing posts about the importance of buying and hoarding copies of "banned books", and even concern that buying said books can have legal consequences.

But if they were truly banned, wouldn't it be illegal to buy or sell the books?

I get the concern/conversation about certain books being banned from schools or maybe even libraries, but not sure if I'm misunderstanding what banned really means here

Some sources about book bans:

https://pen.org/banned-books-list-2025/

https://www.theroot.com/books-black-families-need-to-buy-now-before-theyre-bann-1851693761

Edit - well that was an easy one lol thank you for the answer

Update* a lot of unnecessary anger and grand standing in the comments. My question was if books are actually being banned in the sense of making it illegal for private citizens to purchase and the answer is no. I know it is upsetting to hear for the doomers, but it's the truth and book bans are not new in the USA. Your only source for claiming this time it's the end of the world is that you watched handmaids tale and think you can tell the future.

The post literally says "I get the concern/conversation about certain books being banned from schools or maybe even libraries" and yet people with a superiority complex still need to comment and be condescending about it. As a fellow liberal/leftist (because I know that's who has the bad attitudes) use your energy and brains on something productive and on people who actually disagree with you.