What is the validation criteria for waitlist to say that the idea is worth

I added Join Waitlist form in my landing page and started running ads to drive traffic to it. I see people signing up for waitlist.

What is the criteria to say that the idea is worth pursuing further?

Is it like X% of traffic converted to waitlist users or like X number of users signed up via waitlist?

How did you conclude that your idea is good when you are validating with a waitlist?