The petrodollar is basically a conspiracy theory - you can use dollars to buy oil priced in Euros the same way you can use Bitcoin to buy drugs priced in dollars. Iraq pricing oil in Euros would just mean they sold most of it to countries using the Euro.

The importance of the role of the dollar as a reserve currency is also just an urban myth:

https://www.ussc.edu.au/analysis/the-reserve-currency-myth-t...