Thanks for the request! Your Open VSX namespace is verified and docs.undo.io looks good, but there is one thing missing before we can add the checkmark.
The homepage field on your Open VSX listing (Open VSX Registry) is currently empty. We need it to point back to your website, for example Visual Studio Code — Undo.io or https://undo.io. You can set this by adding a “homepage” field to the extension’s package.json and publishing a new version to Open VSX.
You may want to do the same for undo.udb while you are at it, since you mentioned requesting verification for that one too.
Reply here once that’s done and we’ll take another look.