If we want to go the route of the Responsibility of the Individual: Resolve to not get your political etc. news from social media. Draw a line for yourself: cool to get gaming news from random influencers online? Probably. News about global events? At this point might be better for most people's mental health to ignore them and focus more locally. However, read how to read a book, make your best effort at finding a reputable news organization and check those for news if you must have them. On same vein, if you don't read at least some article about an event being discussed on social media, DON'T COMMENT. Don't engage with that post. If it really grabs at you, go find an article about it from a trusted source, and depending on how much it animates you, try to get a bigger picture of the event. Assume that vast majority of ALL CONTENT online is currently incentivized to engage you - to capture your attention, which is actually the most valuable asset you have. Where you put your attention will define how you feel about your life. It's highly advicable to put it where you feel love.
Responsibility of the Collective: Moving in hierarchies, we can start demanding that social media moderators (or whatever passes for those in any given site) prevent misinformation as much as possible. Try to only join communities that have mods that do this. Failing that, demand social media platforms prevent misinformation. Failing that, we can demand the government does more to prevent misinformation. All of those solutions have significant issues, one of them being they are all very incentivized to capture the attenttion of as many people as possible. Doesn't matter what the exact motivation is - it could be a geneinly good one. A news organization uses social media tactics to get the views so that their actually very factual and dilligently compiled articles get the spread. Or, they could be looking to drive their political agenda - which they necessarily do anyway because desire to be factual and as neutral as possible is a stance as well. One that may run afoul of the interests of some government that doesn't value freedom of press - which is very dangerous and you need to think hard for yourself how you feel about the idea of the government limiting what kind of information you can access. For the purposes of making this shorter, you can regard massive social media platforms as virtual governments too. In fact, it would be a good idea in general.
The thing with misinformation is that many people who talk about it subtly think that they are above it themselves. They're thinking that they know they're not subject to propaganda and manipulation but it's the other poor fools that need to be protected from it. It's the Qanon and Antivaxxers. But you know better, you know how to dig deeper into massively complicated global topics and find out what the true and right opinion about them is. You can't. Not even if we weren't in the middle of multiple fucking information wars. You'd do well to focus on what you can know for sure, in your own experience. If you don't like the idea of individual responsibility though, because "most people aren't going to do it" - your best bet at getting a collective response is a group of individuals coming together under the same ideal. It'll happen sooner or later anyway and there's going to be plenty of suffering before either way.
Reasons vary between people. It's not important. If you want to know, ask the people in question.
Don't think everyone SHOULD be doing it like you. If you feel like being upbeat, be upbeat. ACCEPT not everyone is but they don't get to force their view on you either.
It's naive to think one way is more "right" than the other.