Is Content Sharing broken?

Or is it jus t me?

I have a campaign with Content Sharing enabled. I've specifically disbled source books players shouldn't be able to choose from. And yet, if they choose ie 5e Extended when building their character, they can choose from books I explicitly haven't enabled.

I've enabled TCoE in Content Sharing, so 5E Extended has to be enabled for this to be available. However, enabling 5e Extended, the players can also choose from Xanathar's, Spelljammer, etc.

What am I doing wrong?

Nothing

Disabling books prevents the players from reading your copy, but it does not stop things from being added in the character builder. It was designed for adventures, where you don't want them reading the book, but you still want to give them items.

Aside from the extremely non-granular switches in the character builder, there's no way to stop a character adding shared content.

Ah, thanks a lot, buddy. Have great weekend :) I'll keep an eye out for non-accepted items and spells :)