Five months ago, there was a question posted to EA reddit asking about supporting Russian protestors and whether this was a good cause for altruism: https://www.reddit.com/r/EffectiveAltruism/comments/t5csvr/supporting_russian_protestors_as_the_safest_way/ (I also noticed some interest on this forum as well, e.g. here).
Recently, one of the protest groups that I'm involved with has created a Russian Resistance website that explains what is happening and provides some options to support Russian antiwar protesters by throwing money at them. The Russian protesters are mainly operating covertly, since the degree of political repression has increased drastically since the beginning of the war, but are doing many amazing things.
(Did you know that some brave people have managed to sabotage the Trans-Siberian Railway? And the date of that event was June 29, the Russian Partisans and Underground Fighters Day? Unfortunately, we don't have the technology to safely financially support these sorts of things yet, but it actually looks like a job for something not quite unlike Assassination markets)
Could it help stop the war? Could it hasten the regime change and/or increase the odds of Russia finally moving away from authoritarian rule? Is it more effective at preventing suffering than donating to Ukrainian refugees and/or drafting a letter about new sanctions/arms delivery to your politician of choice?
I don't know, honestly. I'm afraid it's your call to make. However, putting out this information wouldn't hurt, would it? By the way, if you have any ideas or good scholarly sources on tackling this sort of questions - I would be glad to hear them.