This domain is an infrastructure component owned by Yandex, the Russian internet giant behind services like Yandex Search and Yandex Mail. It's not a website you'd normally visit – instead, it's a CDN (content delivery network) used to serve assets for Yandex's UX feedback tool. That explains the 403 error when you try to open it in a browser: it's built for machines, not people.
For anyone wondering whether uxfeedback-cdn.s3.yandex.net is safe to trust, the answer is straightforward. Yandex is a publicly traded company with a long track record. The subdomain uses valid encryption and isn't linked to any scams or blacklists. The lack of an about page or contact form is normal for this type of backend server. If you see this domain when a feedback widget loads on a site, there's no reason to be alarmed – it's a legitimate part of Yandex's infrastructure.