The incapacitated condition states that
An incapacitated creature can’t take actions or reactions.
Does that effect allow you to move though? Moving is not an action (at least not in 5e).
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The condition states everything you're not allowed to do:
Actions (which also prevents Bonus Actions, per PHB p. 189: "anything that deprives you of your ability to take actions also prevents you from taking a bonus action")
Moving is none of those, so you can do it.
Keep in mind, though, that most effects that incapacitate also cause other conditions, such as movement restrictions. For example, hypnotic pattern says
While charmed by this spell, the creature is incapacitated and has a speed of 0.
The thing about 5e and other gaming systems is that they don't always make sense or a rule requires further clarification.
Yes, if going strictly by the book, then all that is affected are Actions, Reactions, and Bonus Actions.
But, if a person is incapacitated, then how does it make sense that they can move their normal distance?
If we look to the definition of the verb form of "incapacitate", we find that it states it is "to make (someone or something) unable to work, move, or function in the usual way"
The key to that definition is "in the usual way". It doesn't say stop moving. It just means that their movement is severely restricted.
So, if we applied the definition to 5e rules, then you could say that an incapacitated PC is still able to move BUT not in their usual way or even distance. Instead, their movement would be very restricted (i.e. 5' per turn by inch-worming, hopping, or rolling their way across the floor).
Technically, you are still following the rule of not allowing them to take actions, reactions, or bonus actions but allowing them to move. You're just adding an adjustment or restriction to their movement rate that makes sense to you as the DM for an incapacitated person.
Remember, the rules are there for guidelines and it is okay if something doesn't make sense to adjust them so they make sense to you and your campaign.