It's not worth $20B, that's just his ego talking. I can see it being worth $4B. It has no long term path to any kind of high growth multiple. Twitter was always an amazingly useful concept but not a big money making business idea. At best it could become like a steady ultility company.
I'm steelmanning my argument. But yes, you're right. I can't imagine a real VC firm buying Twitter today at $20+ B.
Note that Twitter has a $13 Billion loan with $1.3 Billion/year in interest payments in a rising interest rate economy while VC banks like SIVB are failing. That means to buy Twitter at $20B valuation, the VC firm would need to spend $33 Billion. ($20 B valuation + $13 Billion loan)
I honestly don't see this company having enough runway to even reach the $1.3 Billion/year interest payment, let alone the rest of it's liabilities or costs.