23up I doubt many people on this forum have detailed familiarity with Iran's cellular and Internet systems -- and also doubt that any such experts here would publicly give advice.
Perhaps a professional security consultant might suggest GrapheneOS as part of a solution for a specific person in a specific situation -- but in some countries maybe just having GrapheneOS would increase risk.
In general, smartphone operating systems can't work as magical safety shields. If you use Facebook from a GrapheneOS device, you're still using Facebook. If you use GrapheneOS in a country, you are still subject to that country's government.