We have limited data on this. There have been surveys, but survey data isn’t always very accurate.

Here was one survey that showed 81% disapproval of the Islamic Republic: https://gamaan.org/2023/02/04/protests_survey/

In a country of 90 million, if the regime has 20% supporters, that’s 18 million supporters.

Tehran population is 9 million, 20% of that is 1.8 million.

So it’s easy to understand why you might see videos of hundreds or thousands of regime supporters in the streets. That doesn’t mean they’re the majority.