If you really want a chat tool to start a revolution, meet in person with people you trust and don't bring any electronic devices with you. And only talk to people who you really trust. Forget phones.
A antifa relative does not carry their phone with them when they meet, nor do they carry it in their person when attending a rally - they have a friend/lawyer name/number written in a paper with them, just in case some one has to be contacted.
At rallies, masked, sun glasses, baseball hat and a couple of shirts
Not having any communications at all puts you at a massive disadvantage when opposing people who do. Absolutely no revolutions were ever accomplished by improvisational means.
Anyhow, a combination of the two is likely best. It won't really help though, "back in the day" every movement had a few police informants in the mix. There's less of that now with electronic monitoring, and 24x7 tracking, but a totalitarian state likely has more of that mix.
Heck a bunch of crooks tried to rob my house, and were caught not only due to having their phones on them, but ALSO due to sending SMS messages about houses they were examining "This house looks empty!", but also because they dropped a phone outside my house, when fleeing when the alarm went off... and the phone wasn't even locked!
Just imagine in a police state. I think a lot of revolutions get stopped before conspirators even get to the "protect our comms" point.
A revolution is all about subterfuge, intelligence, and trust. If you don't hone those skills, you might not be suited for one. Conversely, technology is an attack vector.
Everything is trade-offs. Meeting in person is great, until you're in the middle of a protest and everyone has to scatter because the police are firing tear gas at your skull. At that point, you rather do need to either have had a plan, or you need some way to communicate that isn't face-to-face.
It was quite remarkable how Jan 6 proceeded entirely in the open with people posting selfies of themselves saying "off to overthrow the government today!", but because that kind of thing is entirely normalized from rightwing sources it wasn't important until those arrested eventually made it to court.
Stochastic terror and the stochastic coup work great precisely because there are no clear unambiguous two-way communication trails between the instigator and the accomplices; just a lot of "wouldn't it be great if somebody did something". Fell apart afterwards because there was no further planning.
At rallies, masked, sun glasses, baseball hat and a couple of shirts