According to an ever-increasing number of reports, Iran and Russia will sign a 20-year USD 10 billion defence agreement somewhere this month. Under that agreement, Moscow would supply the Islamic Republic of Iran Air Force (IRIAF) with 24 Sukhoi Su-35 Flanker-E, two S-400 air defence missile systems and a military satellite.
Although Russia’s main arms exporter Rosoboronexport surprisingly declined to comment on this agreement, Iran’s Mehr News Agency reported that Russia is ready to sell the Su-35 Flanker-E to Iran.
There would be a certain irony to that - so CAATSA kept Egypt from acquiring Su-35s, but possibly at the price of placing the very same airframes into Iranian hands. I mean, you have to wonder where they'd be liable to do less damage to US interests...
US put pressure on Algeria with CAATSA because Su-35 doesn't make sense for me. AFAIK, Algeria air force equipment mostly based on Russia stuff with few west stuff. Algeria get CAATSA because they want Su-35 is like giving Vietnam CAATSA treatment because they buy Su-35. It will only help China find military export customer.
CAATSA is never about the buyer, the intent is simply to counter Russia at virtually any cost. As you can see from the above example, this goal may potentially be pursued to the point of damaging the interests of an actual US ally (Egypt) to the benefit of an adversary (Iran). Algeria (unlike Iran) just has enough economic ties to the US that there is leverage to easily enforce CAATSA, and as it's not a close partner (like Egypt is), there will be even less hesitation to do so.