Aesthetic text uses the Unicode "Fullwidth Forms" block, a set of characters originally designed to line up neatly with East Asian characters in fixed-width grids. Because each fullwidth letter takes up roughly the width of two normal characters, mapping A–Z, a–z, 0–9 and punctuation onto that block produces the airy, spaced-out look people use for bios and captions. It's still real Unicode text under the hood, not an image, so it copy-pastes normally into Instagram, TikTok, or Twitter fields that accept plain text.
The characters come from the Fullwidth Forms block, which was built for East Asian typesetting grids, so every letter renders unusually wide with generous spacing, that visual rhythm is what reads as "aesthetic" or vaporwave.
Yes, these are standard Unicode code points, not a custom font, so any app that can display Unicode text at all will show them, though the exact glyph shapes vary slightly by platform font.
Only the ASCII range (letters, digits, and common punctuation) has a fullwidth counterpart in Unicode, so characters outside that range are passed through unchanged rather than guessed at.