So you want an Adventure or a Campaign?
This time around we're talking about Adventures and Adventure Paths - the latter specifically for Starfinder, Pathfinder 1, and Pathfinder 2.
The reason for that is fairly simple: While there are campaigns for 5e published by Wizards of the Coast (such as Curse of Strahd), they're not really the main thing that they release, whereas Paizo supports its games a lot. We'll also be talking about adventures and paths from other publishers.
So what can you find, and what should you choose?
It mostly depends on your GM'ing style and the time commitment that your players can commit for. You see, everyone has seen and heard of these epic campaigns that stretch across hundreds of episodes (such as those by Critical Role and Glass Cannon), but for many of us, that is simply not realistic or even possible. We have lives, kids, pets, spouses, hobbies and so on, and so on. So what options do we have? Well, one of the things you can do is play one of these campaigns still, but maybe use one of the already existing ones so that you don't HAVE to spend the time planning it all. You still can, but you don't have to.
Then there are the "one-shot" adventures. And I have to admit that I don't like that expression because so many people seem to believe that a "one-shot" should be an adventure that plays out over a single session, and then it's done. But a single session for one group might be 2 hours - but that group gets together every week. Another group might only get together twice per year, but they play for 10 hours instead. That "one-shot" definition would not fit both groups.
Instead, it is probably more correct to call it a "self-contained adventure" and then list an idea of how many hours it takes to complete, based on playtests. (Admittedly, many smaller companies simply do not have the resources to run those playtests, but it should always be attempted).
Then there are the rare (at least I've only ever seen a few) "episodic" style games, and they might work well for people, but I've not seen many (if any) companies build upon that idea. Those are the adventures that last a single session (and on rare occasions two), but which work like a TV-Show such as Star Trek: The Next Generation, where there's a new adventure each time, but using the same cast of heroes. These would work well for certain groups, and can (if done right) all tie into a longer-running campaign or campaign-arch with an overall theme, while still having time and possibility for the heroes to go off on a wild goose chase for an adventure or two.
Over on Nerds on Earth, they were kind enough to make lists of all the available adventure paths from Paizo, which you can find here:
Have a look at them and see what you like.
Or you can take a look at what we have here at Beyond the Horizon. We hope you enjoy the offerings. :)