for devs/builders, a landing page with real copy and rough roadmap is plenty, you’ll get feedback way before launch.
for consumers, though, everyone’s spoiled. if there’s no demo, no dogfooding, they bounce in 10 seconds.
tl;dr: test your copy/ideas with a page, but have a working click-thru demo asap if you want anyone outside your bubble to care.
no-code tools make it too easy for the next guy to show something.
Dev tools or B2C: landing page (collect email) with app/product tour video or mockup screenshots
B2B: landing page with video or mockup screenshots, and 'book a demo' link/form (collect as much info)