That's a very weird take I see repeated over and over again
You don't protest only to get your government to do something, the protests against Israel expectedly did not meaningfully change US relations with Israel yet you still presumably went out
you can express solidarity with Iranians, you can protest the massacre, or just make people be aware there are thousands dying
Sanction them? To stop sending them weapons? Isolate them diplomatically?
Surprisingly, all is done already
As long as Iran has multiple countries it can sell its oil, there is still pressure to apply
The real reasons there are no protests are in my opinion the same ones people generally suspect
For example I don't believe the US saw particularly large scale anti Germany protests surrounding WW2. Before the US joined the war people didn't really know what to do, while after they joined the war there was little disagreement. The Vietnam protests were much larger, because you have the internal conflict and something obvious to do: stop fighting.
People showed up for Gaza protests because they were angry and because they felt people around them, and particularly their governments were complicit in events. People do not show up for Iran because everyone agrees it's terrible but no one really knows what to do, so who are you going to be yelling at on the streets and what would you yell? Additionally events in Iran, relatively speaking probably triggers more hopelessness/confusion than anger, these are not exactly the best emotions to inspire protest
You are not convincing China to only source oil from western aligned nations.
We (Europe and US) can't even convince India.
Short of kinetic intervention. There isn't much to be done about Iran.
I doubt bombing Iran will make the protesters in Iran more successful or united.