That's what I like about Pathfinder 2E. There multiclassing (or a Dedication, as it's called in that system) can be done by just taking the one feat (the original Dedication feat) but that often gives you the just the basic ability of that class at the lowest level and that level won't go up as you level up, so by the time you're above level 10 it won't do all that much anymore.
For instance a Wizard Dedication gives you the ability to cast 2 cantrips and makes you trained in spellcasting. But that gives you a level of spellcasting that you won't succeed against the saves of any critter at level 10 or above most of the time.

So you need to take a few other abilities from the Dedication to make it actually work, especially at higher levels. As you need to take 2 dedication feats, which you take instead of class feats before you can switch to another dedication and you get a class feat at every even level (generally), that's a 6 level commitment before you can switch to something else. So you will most likely not take more than 2 of these dedications and most likely only 1. You also keep getting the non-class feats of your original class, no matter what Dedication you take.

And it's a lot easier to explain in character. For instance a rogue with wizard dedication is simply a rogue who also studied magic at sometime, but he stays a rogue. If you take just the Dedication, you're a dabbler who learned a few simple tricks at some time and if you invest the time to take more dedication feats, you invest time and energy in becoming better, as you would if you multiclassed evenly in PF1.