Iran is nothing like Iraq. Iran's military is very advanced, with technology that could blow our best naval ships out of the water and rumors that they have air defense systems to counter the B2 and F35. We know they are getting the SU-35 fighter jets from Russia, which would also take away from our air superiority. Iran's military and country is also much larger, about three times the size of Iraq's, with a terrrain that is nearly impossible to take via land, which is why they have held it for thousands of years.The United States militarily defeated Iraq in a matter of days, maybe a couple of weeks.
VIrtually all of the casualties were during the ensuing occupation as the result of the insurgents utilizing guerrilla warfare, the use of IEDs, etc.
I do not believe Iran would be much different in that the US military would decimate the country's military and strategic infrastructure in a very short time, and then seize control of Tehran.
The question is what then? If the US tried to occupy Iran for years or decades on end the cost in dollars and lives lost would be astronomical.
And the USA military of 2025 is nothing like the USA military of 2003.
I would at a minimum expect Iran to win, and potentially Iran eventually finds ways to attack our infrasture in a way of revenge and making sure we never come back.
And that is even if China, Iran is China's biggest supplier of oil and Russia (direct hot war with NATO) decide to stay on the sideline and I have no idea why they would do so.