What Books do you have to buy to unlock something?

I know that you have to buy Tasha's Cauldron Of Everything to make an artificer on DnD Beyond, but are there any other books that you have to buy to create specific Classes/Subclasses or even Monsters. I think Monsters of the Multiverse gives you some monsters to use if im correct?

Also correct me if I am wrong, but if the DM has bought some of those books, he can give access to the players who play in the campaign, so they can create for example an Artificer

Edit: I've been looking around some more and saw that a lot if not every book adds monsters and other stuff, so another questions from me is, what are the most important books or what books add the most stuff to DnD Beyond, like for example Tasha's Cauldron Of Everything adds the Artificer class, which I think is pretty great.

Do you know if you need to buy specific books to unlock more Critical Role Classes, etc.? Because I don't think that it only gives the Blood Hunter class

The Blood Hunter is free content.

 Quick question, does the Dungeon Master's Guide, the Players Handbook and the monster manual add anything to DnD Beyond that is otherwise not available to people who dont buy the digital books?

Hey there, just wondering why I can't access all the Wizard "school" subclasses. My DM has all books available shared and i have them downloaded, I'm trying to make a Divination Wizard but it only allows me to make an evocation school subclass. Like that's my only option