I thought this was largely fake news that crypto sites were generating. That specifically, the US and KSA are just in the process of hammering out a new agreement. And that even if some oil contracts are in other currencies, they are still indexed to the USD.
The news about a 50-year old petrodollar agreement expiring that's been spreading through social media is completely made up. I think it was "BRICS News" on Twitter who first posted it, and that account is known to post fake news and never links to a source.
They could just play the US and China against each other to get the best deal out of each. That's typically the playbook for regional powers in bipolar and multipolar settings.