Wanted to know if there is something like "design validation" similar to "idea validation"? or the terminology is wrong?
If you know any similar website or app please let me know.
In the design world, this is known as "user testing". There are a variety of ways to test design but no better way than watching someone else use your app/design/prototype and talk their way through it.
Having them voice their reasonings for actions/paths taken allows you to prioritize the user experience so you're not just guessing in a vacuum what the user should or shouldn't be doing in any scenario.
Do this process with a handful of folks and get a median amount of results to determine if your design is working or not.
You could try usertesting.com if you need quick feedback.
There is landing page feedback hashtag here. The problem with design validation, much the same as idea or landing page feedback is that you rarely get input from your target audience, and when you do, it’s biased by default since you had to ask in the first place.