I see the only succesful way to invade is first take the small islands and then the large one of Qeshm, there is a large community there, declare it "Free Iran" and let a provisional government form from the locals and Diaspora. Now a lot of the Iranian coast is well within FPV range and you can make it untenable for the IRGC to fortify it. The image below is what the west can strike with 50km FPV drones
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Form a force from liberated and overseas Iranians to fly the drones and take part in raids along the coast. Slip operatives ashore and start arming the people against the regime. Be very careful in your targeting and try to have an Iranian face on the missions. Out of the 90 million people who are not IRGC/supporters/family you can like rise a sizable force and slowly take the coastal area and proceed with having the Iranians take control. Allow regular Iranian military to defect and join the Free Iranian Military (FIM). Work at taking control of areas using the locals and with as minimal force as required. Set up a prison so low level IRGC can surrender and be held in safety, until they can be either deradicalized or stand trial. Bombard the air waves/social media with messaging about the liberation of the country. Do everything to fracture the current ruling regime, from targeted hits, to blackmail, tainted intelligence to get them to kill each other, bribes, offers of safe passage out of the country, etc
US forces provide support, logistics and firepower and other than SF, generally stay back and minimize targeting of US personal. Once you gain a port on the coast, expand the FIM and provisional government there