No matter what you perceive, you are the only one who can perceive it.

You can verify that there are others around you and that they too are capable of perceiving, but even there still, it is you who is perceiving the idea that they are able to perceive.

No matter how many people there are in the world and no matter how many people interact with you, you are the only one who is perceiving your experience. No one else can do it for you and you can't do it for someone else.

And if someone walks up to you and tells you that they can perceive your thoughts and they prove it, that still means that you are the one perceiving what they have told you about you.

So do these others exist? Yes. Are they truly perceiving their own reality? Maybe. You cannot know that with absolute certainty unless you are that person.

Wether you really are the only one or not is not the point. The point is wether or not you can cope with what you can perceive.