Link a domain with a DNS record or a small file, a website with a tag on its page, GitHub with a public gist, Bluesky or Mastodon with a code in your profile, or Steam through its own sign-in. Each linked account arrives with a verified tick and Show on profile off; turn it on and it appears on your profile card, only to the people your profile privacy lets see your whole profile. Remove takes it away at once. Nothing is ever posted to the other service, and the privacy policy says what is kept.
Connections in Kemble Circle: show the accounts you have elsewhere
User settings › Connections links your domain, website, GitHub, Bluesky, Mastodon or Steam to your profile, proven yours and hidden until you choose to show it.