The EU is their primary customer

Russia's Largest Oil Company Ditches Dollar In New Oil Deal

Russia’s largest oil company Rosneft has set the euro as the default currency for all new exports of crude oil and refined products, as the state-controlled giant looks to switch as many sales as possible from U.S. dollars to euros in order to avoid further U.S. sanctions against it.

So this makes sense.  The risk of holding dollars is small but positive.  If you major trading partner has a nearly stable currency, use it directly and avoid the extra insurance cost.  The ruble becomes kind of a carrying currency between euro and yuan, where Russia's other major trading party is China. Iran should quit manipulating currency and join the party.