The author of above video mentions some privacy concerns in regard to creating an account with NextDNS,
Every DNS out there logs data, even no-log like Quad9 or Cloudflare, because of DDoS protection and they mention it in their Privacy Policy. The only difference is, how fast they remove logs, some after 2 hours, some after a few days. It is like arguing whether you should have Google/MS account, if you do not, they will log your data, if you do, you can remove it at your discretion.