For the OP (and others):
I love Foundry and I like pushing it whenever possible. For this use case it's not ideal if they aren't actually playing in Foundry. I was going to recommend Nexus Demiplane, but I just realized something: Both VTTs I have experience with - dndbeyond and Foundry - gate your character options to books you've purchased. I imagine Nexus, FantasyGrounds, etc all have to do this as well for SRD reasons.
So I think your best bet would be to use either the official fillable PDF from WoTC OR one of the thousands of user-created fillable PDFs.
As for the OP's reason for leaving dndbeyond - it's been a while since I dropped my dndbeyond account - not for any principled reason - it just didn't make financial sense for me. I like playing different systems so it's better to buy my books on a neutral VTT instead of D&D's VTT. However, did they give you a field for saying why you left? Otherwise it's a very indirect protest that doesn't necessarily tell WoTC they shouldn't make deals with Rowling. In other words, if WotC made a Rowling D&D module and no one bought it - that would tell them people don't like the Rowling deal. If, all of a sudden, people stop buying the Artificer module because of the Rowling deal, they might just think people don't like Eberron. This isn't me telling you how to protest, just that it's not really doing anything if Hasbro/WotC doesn't understand why you left.
(edit for punctuation)