First of all let me say right out of the gate that ideas are overrated. Having a lot of ideas is good, having good ideas is even better, but they're not even half of story, which is why I always find it funny when people want me to sign an NDA before sharing their idea. The likelihood of anyone trying to steal your idea is very low, the likelihood of someone trying to steal your idea and then doing something useful with it is even lower. All of this to say that the hard work happens after you've had the idea, not before!
"It's not the idea, it's about its execution" is already a cliche at this point and even though I mostly agree with it, I think it can be misunderstood. What it is saying is that good execution is paramount if you are to make it, it is not saying that the idea does not matter, it is also not saying that you should jump right into execution. The latter being what we engineers tend to do.
Ideas matter, because you've got to start somewhere. However, they are most akin to a diamond in the rough, only after you cut and polish it do you know if you've got a precious gem or little more than a rock. Moreover, cutting an polishing is a hard process, which may take years to learn how to do right. A lot can be done with simple common sense, especially if you are a possible customer for your product, but for most people there's a limit to how much you can take out of that.
"So now what?", you say, "I have this great idea that I want to build. What should I do?"
Validating them matters more
After you have your great idea and think it through for a few days, it's time to see how it fares against the real world. There are multiple ways that you can do this, but at this point very few will be better than interviewing people that match your target (people in general is a close second). You can more or less formally define personas, the gist of it being that you imagine a person, with all of its traits, that would be a client for your soon to be product. Then, as you go through the nuances of your idea, see if it matches the needs of that persona. Would they buy it? Would they use it? Be very critical here.
Even with as little as 5 interviews you should have gathered tons of information. That information should allow you to more clearly understand if you have a good or not so good idea, as well as where it needs a little bit of cut and polish to become better.
Now, there's a lot of different types of interviews and a lot of things to consider when preparing for them, especially if it's your first time doing this. You'll have a natural tendency to tell them about your idea and ask for their approval, "Would you like X?", "Isn't Y a pain right now?" or even "Would you pay for Z?". These are all terrible questions. You're putting the interviewee in a position in which they will say what you want to hear. Instead, don't talk about your idea, don't even mention you have one, at this point all you care about is understanding if it makes sense. Ask them about what they feel about a topic, how have they solved in the past, have they tried to fix it?
Want vs Need
If you follow those rules and are true and honest about reading the results, you should be able to understand a key question in validating any idea. Is this a want or need, aka is this a vitamin or an aspirin? The answer to this question will dictate a lot of things. If it's a want/vitamin it'll be a harder sell with a smaller market, no one really needs it, it's something they might buy on a whim, or if for some reason they happen to have an issue and disposable cash at the same time, but you'll be on thin ice most of the time (named brand can be seen as a caveat to this, since you could get it cheaper, but I'd argue people buy it for a need of social acceptance and acknowledgement, be it to show off or because it's part of cause they believe in).
Ideally you want to be in the realm of what people need. That's the aspirin, that's what people will pay good money for, even when they might not have that much disposable cash, and for good reason, because it'll be a priority for them.
Problem vs Solution
On the same spectrum of want vs need there's also a very important concept to keep in mind when validating an idea. Is there a problem here, or only a solution? Time and time again you'll talk to people with brilliant ideas of how they'll build something, only to realise that even though it sounds good, what they have is a solution to a problem that doesn't exist.
At this stage, the solution is secondary. You can always pivot, change your solution to something slightly (or not so slightly) different, as long as there is a real problem behind it.
There are many ways to validate this as well, and interviews can always work, but in my experience at this point what you should be doing is running a design sprint. Incredibly so, a design sprint has very little to do with what you'd call design and very much to do with design thinking. It will help shape how you think. There's a multitude of resources online about them, but their a bit scattered, in my opinion, also most resources will focus more on the structure of the sprint as opposed to how it should be ran and what you should be looking for while running it.
Having the idea is only the tip of iceberg, there's a lot more to be done before you can confidently go to implement a possible solution. There are many options to validate your idea, understading which to employ when, and how to employ them requires a lot of experience. If you can pair with someone that has done this validating successfully in the past, do it, but most people can't, so inform yourself the best you can and try anyway.