Help training puppy to not freak out when seeing new people or dogs

I just bought my first puppy (poodle) a few weeks back, and he is now 11 weeks old.

We are having a lot of success with potty training, tricks, and crate behavior, but are really struggling to limit the dog’s reactivity.

I know puppies are just excited in general, but when we see any human or dog outside (I live in an apartment), he absolutely loses control. He flails around in his leash attempting to run to them, and will not settle down even after they are out of sight.

Does anyone have any tips for calming their puppy when encountering people or dogs?