Meanwhile RUB to USD is at its highest in nearly 5 years. Cutting Russia off from SWIFT has only strengthened their ties to India and China. Russia is still invading Ukraine, and now we're dealing with soaring food and energy prices at home. At some point you have to consider whether this level of diplomatic incompetence is intentional.
Since RUB exchange is so constrained, its "market rate" is also meaningless. I too can issue a currency, set its value at 1,000,000 USD per unit and declare monopoly in trading it.
There are plenty of Forex exchanges trading RUB for any currency. Including USD, EUR and others. Governments don’t have control over all exchanges so they can’t set the price. The price is determined by supply & demand (ie: the market). Governments do have some levers they can use: buying or selling reserves to put up or downward pressure on the market price.
To limit trading of a currency you’d have to limit exchanges to any other currency. If you limit RUB-USD for example, people could still trade RUB-EUR and EUR-USD, thus still creating a defacto RUB-USD pricing.