If the Saudis started selling oil in bitcoin they'd probably lose their military support and/or be overthrown.
It is difficult to justify why the US is providing militarily support to the Saudis without invoking oil and dollars. They are a pretty shady regime and not the sort of people the US wants to be supporting. And the Saudis don't seem to be trading with America as much as China [0, 1].
While the term "petrodollars" makes sense prescriptively, saying that the KSA would be "overthrown" if they started settling transactions in something other than dollars is pure hyperbole. The macrobullshitters that keep throwing around this idea of ongoing US coercion are doing so with absolutely no proof. Sure, there's some soft power things going on, but they settle in USD because USD has been the de-facto currency for world trade (and thus currency reserves) for some time now. IF anything, we see a movement away from USD into a currency basket with a high weighting of USD over the coming decades.
Decisions and strategies worldwide do not make sense if you don't acknowledge that such things happen. That e.g. an oil country moving away from the dollar is something the US would do nasty things to avoid - and the reasons for that fall in the category of "conspiracy theory", but that is the case because no official tale makes sense. You know it is not about the weapons of mass destruction, because these were proven lies, and you know they did not tell these lies to "save the people from a despotic regime" after decades of "we don't care", because there are other examples of despotic regimes (including KSA) the US does not bother or has friendly relationships with.
So, what would you think is the reason the US invaded Iraq?
Do people not seriously think about why the Iraq war happened? Everyone accepts that the WMD rational was disingenuous, so then why?
It just so happened to coincide with Saddam starting to sell oil for Euros, and France and Germany just so happened to oppose the war.. but it's probably nothing to do with oil and dollars.
Gaddafi wanted to sell oil for Gold. In that case Europe and the US were on board with removing him. Why then, when he'd been in power since the 70s?
The Saudis are also well-liked by the US and much of the Western leaders because they buy billions in arms. Nevermind the crucifictions, decapitations, and dismemberments.
Reminds me of one of by favourite Frankie Boyle jokes: "Our government was angry about Khashoggi. We sent the Saudis a strongly worded arms invoice."