Nine year redditor here; I never fell into the doomscrolling that so many others talk about, and I will miss Reddit, but something I've discovered is that while it's difficult to get a "toe hold" in the fediverse, once you do, there is way more content here than I ever knew about on Reddit.
Not saying that Reddit didn't have it, but rather that I never got curious enough to poke around beyond my main block of subs that I'd curated over that decade. There are entire domains here devoted to science or philosophy or retro gaming, and it really does look like they're vibrant and active. Finding them is the issue, which really is the big problem with the fediverse in the first place.
There really isn't a great cut-and-switch over to Lemmy that will make a redditor feel like nothing has changed, but the discovery process isn't too much different from Reddit, and I think people need to remember that their Reddit experience wasn't built in a day. My suggestion is to take a more curious approach rather than the "Reddit's dead, what's its identical replacement?" that I see, because there really isn't one and, even if there was, it'd be just as susceptible to the same disease that is currently killing Reddit (and Twitter).