How can I disable or remove Tasha’s Cauldron of Everything? I play with a DM who does not allow this content anymore. I’d prefer to use D&D’s beyond character builder, but I’m not able to as D&D beyond automatically incorporates this content since I had purchased this compendium several months prior.

 Don't use OCFs or TCoE subclasses and spells?

You cannot. Now that you have purchased it you can never disable those options.

On the Home tab of the Character Builder, make sure the Optional Features switches are turned off. 

So yeah, in the character builder make sure "optional class features" and "customize your origins" are turned off.  As for subclasses and spells you just have to read the subclass and spell and in fine print at the bottom it will show you what source it's from.  

Quote from jdahveed >>

On the Home tab of the Character Builder, make sure the Optional Features switches are turned off. 

 Those are switched “off” (grey, to the left) by default.

Tasha’s is considered core content. I have optional content turned off, and it still pulls in content from Tasha’s Cauldron of everything.

Can you specify what is showing up? It's a known issue that fighting styles show up, is it that or something else?

The problem isn't the lack of content from Tasha's - it is quite the opposite. A simple example is that the Soul Knife subclass is an option that my DM doesn't allow.