lol no. Iran hasn't yet been able to enrich uranium to the necessary purity to make a bomb. Yes, making a bomb is easy once you have the materials. Getting the materials is very difficult. If by "dirty bombs" you mean a conventional bomb with radioisotopes mixed in... well, the use of that kind of weapon would probably get Iran invaded, but since it's not a very practical weapon it wouldn't affect the strategic situation.
Nuking Iran was never in the cards. We could have done that in 1979 and any time since. Ukraine has nothing to do with it. The red lines that would provoke a nuclear response from the US are pretty well known -- the US foreign policy establishment hashed out this stuff 75 years ago. Iran could get nuked by the US if it used NBC weapons against the US or our allies. No amount of bad behavior with conventional weapons is going to do it.
People in charge of nuclear armed countries are worried about the end of the so-called "nuclear taboo" which has kept countries from using nukes for 80 years, and they're not going to break it over a third rate power like Iran unless that third rate power actually acquires nukes and makes a credible threat to use them. We didn't use them in Korea or Vietnam. We didn't use them in Afghanistan. We haven't nuked North Korea. All more serious situations than the one in which we find ourselves today.
When somebody finally does break that taboo the world will be a much, much more dangerous place for everyone and planners in places like Washington, Moscow, and Beijing know it. Once a nuclear weapon is used, especially by a country with a large arsenal, every country that could have nukes but doesn't is going to have nukes.
Here's a good video on the topic concentrating on the possible Russian use of nukes in Ukraine:
https://www.youtube.com/watch?v=sxOO0hCCSk4