Totally valid as long as you communicated this feeling with them. Could be direct or subtle! Just don't leave them hanging without an explanation. Also, having a company doesn't hurt either! It helps when you have someone you can depend on for a little while. But the choice is still yours ^^
It's completely fine to uninvite a friend because you were feeling depressed. Just make sure to let them know that you weren't doing well mentally so they don't misunderstand, and you don't have to go into detail about it either. Don't think about whether you would have been good company or not, but rather if you wanted company at that time. A good friend will always try to understand your situation, so prioritize your health and try your best to communicate with them.
Not manhwa related but a bit personal.
Does it make sense to uninvite a friend just cause you suddenly feel really depressed? I didnt feel like id be gold company since i was at a very low point. But maybe they couldve helped me feel better? Idk...