Write out your idea. You can start by validating your idea by making sure your answering the right questions. Then you can reach out to people, you don't necessarily need a landing page but a demo probably helps.
I typed out my idea on a Notion page, did market research, existing competitors, and all that. It looked quite promising to me.
I included a small demo on my landing page as well. Maybe I should try reaching out to people with a better functional prototype.
Thanks for the suggestion!