Let's assume this is true.
Nearly all of that hypothetical wealth would be amassed at the very top of the power structure, just like we see in other resource-rich mafia states.
Iran is a major energy producer, and it would make sense for electricity to be provided "below cost" when that cost is theoretical and pegged to the market price of fuel (ie, opportunity cost), rather than the true production cost of electricity.
On face, I strongly doubt the narrative that crypto mining is the cause for any kind of grid failure. The regime in Iran defaults to lies and disinformation when covering up its own miserable failures. Remember when they initially denied that Iran's military had downed the Ukrainian plane? Same deal; they lie until they are cornered. I am more inclined to believe Ziya Sadr.
For Americans who don't understand Iran's regime, compare it to Trump's cries of election fraud; the claim is intended to point a finger that distracts from the actual problem (him losing the election fair and square). The blame in Iran is always placed as far from the leadership as possible, even for centrally managed utilities like the power grid.