They are regional indicators, groups (usually pairs) form the flags, which are in fact multiple characters but behave like a single glyph in a text editor . Use the Irregular Expressions keyboard.

For people using Lemmy clients that only show usernames, @[email protected]’s display name is “🇰 🌀 🇱 🇦 🇳 🇦 🇰 🇮”. Without spaces nor zero-width non-joiners, the name becomes “🇰🌀🇱🇦🇳🇦🇰🇮” (LAos, NAmibia, KIribati) - you can copy the text into an editor, delete the spaces yourself and see the flags appear.