The weirdest problem I see with this conspiracy theory is that I don't see the actual conspiracy?
Like, USD is a fiat currency, it's backed by taxes. The only difference between a paper dollar in your hand, a dollar in a traditional bank account, and a dollar on the hypothetical FedCoin blockchain is how easy it is to spend, what gatekeepers are involved, and what anti-fraud/anti-theft tools you can avail yourself of. Moving from a traditional bank account to a CBDC doesn't make it any easier for the government to seize your funds - they already can do that just fine with basically anything.
I believe the conspiracy portion of that theory is that the financial crisis would be triggered, or allowed, intentionally to create the excuse for a CBDC and fed bank.
I don't see it as likely, just a theory I've seen floated.