while the ruble has never been higher

Its never been higher because the Russian government pegged it to the value of gold. As gold goes to the moon, so does the ruble.

and the russian economy is flourishing.

Parts of the Russian economy are flourishing. Its energy sector, which has been spared sanctions as well as seeing peak demand, has never been better. The rest of the economy is suffering. But that doesn't matter since energy is such a large portion of Russia's economy, that energy is carrying the weight of the rest of the flagging economy.