Depends on how much compute there is to mine it. Not that many valuable cryptos still use GPU PoW. You also need a counterparty to actually profit from it.
Oh man if Elon had billions in H100s we might actually see that happen. And I’m no fan of Elon but I’m also no fan of cryptocurrency these days. Might be worth it just to watch the crypto world burn.
A successful 51% attack on a major cryptocurrency would not necessarily be that impactful. So what if Elon can doublespend? He would need a lot of crypto, a counterparty, and the strong desire to waste money. Large miners could already collude to do it, it just is not in their interest.
Shorting Bitcoin has been possible for a decade now. The capex to pull off the would be in the billions though, and the value of that investment is tied directly to the price of Bitcoin.
That said, the attack you describe has happened for much smaller cryptos. I'm not saying it can't happen, I'm saying there's no reason to assume it would be a huge threat to Bitcoin, because the actual risk for a user is vanishingly small. There are much bigger threats to Bitcoin's valuation that are far more plausible, such as government crackdowns.