If tankies claim to be commies, then why do they support Iran and the former Syrian regime which arrested and tortured communists?

At this point it's just "US bad", Iran and Syria arrested thousands of communism supporters and tortured them, even the USSR supported Saddam against Iran for that.

Also they seem to hate Islamists and justify the Uyghur genocide and Bashar bombing over 500k people, so why do they support Iran?

It's funny that if they actually lived there, they would be sent to Sednaya.