What platforms do you use to get feedback on a website/ lander and so on? Avoiding typical answers like Slack, discord and facebook which it's full of fake profiles.
The platform does not matter. All you are doing is naming different social media platforms, as if though they are the ones who provide you with your audience. Thats not true at all. If you want honest feedback from people who are interested in visiting your website then you must first procure an audience of such people. And it does not matter if its on Twitter, Facebook, Slack, Discord etc...
Do some marketing research, come up with a decent marketing strategy and gather an audience. The rest will come on its own.
The quick and easy way to get feedback is to pay/reward people for it. You can do that anywhere. Even on this forum. Just offer a few dollars in Bitcoin to users on Bitcointalk and they will give you an analysis. Although I am pretty sure that many of us are willing to do so for free. Just create a topic asking for feedback.