Frame shift - Challenges Ahead:
I think what you are looking for is an alpha reader. You'll find different interpretations of an alpha reader, but MY understanding is that it's typically someone who reads your material while you are still writing it, and gives you chapter-by-chapter feedback. Some people find this helpful, while others feel it is invasive to the process. An alpha reader is almost a co-author in some cases.
It's usually very personal, and I wouldn't recommend just going on a public website and leaving your ideas out where people can pick at it. For questions on sites like this, they are very directed. Internet culture is a funny thing. Also, if someone loves your idea, there is nothing you can do to keep them from taking it and rebranding it as their own (especially at the early stages where the final destination is unsure). But maybe I'm paranoid. What IS or ISN'T seen as dependable on the internet is highly variable and subject to opinion. Don't take any one person's word about what is good or right, but look for a consensus. That's why recommending specific sites is a bad idea (IMOHO).
If you are willing to pay money, you'll have no trouble finding people to do it, but validating their qualifications is hard. If you have a local literary group/club (here in Minnesota, there's a group called the Loft, but there are similar groups around the country/world) they often have resources available and can vouch for folks to contract work through. Some writing conferences will have someone who will do an analysis of a part of a book, and a lot of these conferences also have many helpful classes on things you didn't even know you needed to know. Naturally, most of them are on-line in the land of COVID.
I personally have lots of vision (which needs toning down), and would find the judgement of my stories early-on confusing and upsetting. But if you'd like an alpha reader, find someone you know and trust. This can be a friend who shares common literary interest or a teacher or professor willing to put in some time. Really close friends and relatives aren't so good - you can't trust them to be impartial. On the other hand, a close friend could be more like a collaborator, and the fun of something together might be a great experience. The closer a person is to you, the more likely they will be willing to make a commitment to working with you and stick with it. The most important feature in my mind is someone who will follow through, so pick a dependable person.
Hopefully, someone has some great advice about websites, which I can't/won't suggest.
Beta readers, on the other hand, read after you've written, and look mainly for structural problems with the story (things that don't make sense, characters that disappear inexplicably, boring parts that don't contribute to the overall story). While looking for an alpha reader, those same people are the ones you are likely be looking at as potential beta readers. These folks read your story/book and give opinions. You will often give them a list of your questions/concerns about the story and ask them to answer them. There is some commitment for all this, but less than an alpha reader.