What do you do when you truly think you found something you want to build but you don’t know how to get it validated?

I’m new to the entrepreneurship game and looking for some advice

I have this SAAS idea that I think is a pretty decent idea, it’s in a rapidly growing market, I can visualize people using the tool to make money and free up their time

The only problem is trying to validate ideas now a days seems pretty difficult, most subreddits either don’t allow you to or places where you know they would hang out don’t allow posting that kind of thing

So how do you guys go about validating ideas? Is cold emailing/dm’s the way to go about it now? Or building a YouTube community slowly over time?