Yes, the question is what such a system would look like. E.g. would there be limitations of free speech?
Rather what you need is a means for propaganda to be rapidly identified and refuted with counterarguments in a way that its would-be victims can see it.
This is how populism works.
We already have largely decentralized speech in the US via the internet. And much like how the printing press gave everyone a voice or how radio created Hitler, the internet is the modern age vehicle of populist messaging.
The reason someone like Trump can rise to power and consolidate said power is because he speaks simple and lies work in a decentralized system. Populist messaging is built on the fact that humans are naturally drawn to simple solutions and emotional responses. 90% of the time throughout American and European history, if you just tell people "this is ethnic/racial group X's fault!", that works.
Meanwhile the centralized platforms then have the incentive to maximize engagement and the power to structure things that way. And that's how you get Trump, because polarization drives engagement.
Only if you ignore everything about what got Hitler elected.
"Populists" winning is ALWAYS a result of the status quo being unacceptable to the general population. If the establishment is unwilling to fix that then they deserve to be removed from government. Free flow of information isn't responsible for that.
If you have a centralized system with Sean Hannity getting on the television and saying things which are clear, simple and wrong, you still have the exact same problem. Decentralization can only improve it because then it's not only him and the more complicated truth is at least available instead of the simple lie being the only thing on offer.
And this is what I mean by "in a way its would-be victims can see it".
People don't have time to investigate every throw-away simple lie, but it gives you the opportunity to sample. You follow Bob and he says a bunch of stuff and every time there is a whole complicated discussion that you usually don't read because you don't have time. But once in a while you do.
If every time you do, it turns out Bob is right, you can be more confident that the stuff he says is usually right even when you don't have time to check. If every time you do, it turns out Bob is wrong, the opposite. It provides the opportunity to evaluate credibility.
But that only works if you have a system where anybody can reply to anything and actually be seen. If you have a system where a central gatekeeper can make criticism and counterarguments invisible, you lose.
That's why we are where we are, because "both sides" want to have that control, they just want it for themselves and not those that disagree with them.
Counter to the above is that, your bad actor may be my leader. People like convenience. When someone is expressing what you want to say, in a better and smarter way, you just reshare/retweet them. And the 'other side' will feel like your leader is a 'bad actor' who is flooding the system. So even the method of resharing/retweeting needs some sort of provenance/single use only. So you can 'agree' with your thought leader, but they shouldn't be able to mass manufacture consent. Since you might even reshare 'fake news' since you generally trust your leader. It's messy, not sure what that would look like - every post that starts getting traction needs to be fact checked? Community Notes on X is a step in the right direction maybe.