Where fancy fonts work on Instagram
Fancy text works in your Name field, bio, captions, comments, story text and messages. Your @username only accepts letters, numbers, periods and underscores, so it has to stay plain.
Keep people able to find you
Instagram search matches plain letters, so a name written entirely in fancy text is harder to find. Keep your real name or brand in plain text in the Name field, and use fancy text for the rest.