Unless they changed things recently, limiting something under content sharing, only precluded other participants in a campaign from reading a specific source, but all the rules options remain available for characters.
This is correct, and terrible.
The only way to limit sources in the character builder is by going into each individual players Manager and toggle sources in the first tab, repeat for every character in the campaign. This can only be done after the character already exists, of course, so it's basically impossible for a inexperienced user to create a character using only the sources the DM wants used. DM then needs to meticulously review each character sheet to weed out stuff from unwanted sources.
There is also no way whatsoever to bar 2024 classes and spells from selection. Players just have to know not to use them.
For me, the character builder was - or used to be - the biggest value in DNDBeyond. I consider it a mess now. That's not even taking into account the way that they don't even bother trying to implement all the third party books they're now selling into the character builder. If you own the Lord of the Rings book on DNDBeyond, try using DNDBeyond to make a character using the rules in it if you'd like to feel crazy.