A check failure (❌) indicates that your browsing data could be vulnerable. An unwanted party could see sensitive information such as which sites or servers you are visiting, or the certificate you are using. If the DNS response is fraudulent, you could also end up visiting and/or providing data to an unintended party.
A pass ✅ indicates that your browser or DNS resolver supports that particular feature.
Not necessarily. Even if you pass all four tests, the domain you are visiting also needs to support these technologies. If the domain you visit doesn't support DNSSEC, TLS 1.3, and Encrypted SNI, you are still potentially vulnerable, even if your browser supports these technologies.