How would decentralization make a difference here? Fact checking only makes sense when a platform has people with multiple different beliefs about what is true. If people can self-select into their own bubble, then it doesn't do anything, does it?
Right now, the rich leadership of these social media networks are kissing the right wing ring, so get ready to be right winged for at least 4 years.
It's not healthy.
If we didn't have single owners of these platforms, then none of this would be happening.