The 30-second version, then the slightly longer one.
Your keyboard's letters are Unicode characters. So are thousands of other symbols that look like styled letters — a bold 'a', a script 'a', a circled 'a', a wide 'a'. A fancy text generator just substitutes one for the other. The result is still text, so it copies and pastes everywhere; it's just made of different characters than you typed.
Unicode has whole alternate sets of A–Z and a–z built for math notation — bold, italic, script, blackletter, double-struck, sans-serif, monospace. Generators map your letters onto these. Quirks: most of these sets are letters only, so numbers and punctuation stay normal. Some sets are incomplete (small caps is full, but the superscript and subscript 'alphabets' have missing letters that fall back to normal size).
These styles don't replace your letters — they bolt extra invisible-on-their-own characters onto each one: a 'combining long stroke overlay' for strikethrough, a 'combining low line' for underline, and a big random pile of diacritics for zalgo. Your browser stacks them on. That's why zalgo can be made arbitrarily intense, and also why some apps cap or strip it — too many marks can break a chat layout.
These are characters that were designed wide (for mixing with Japanese kana) or inside a circle or a box. There's a full set of full-width Latin letters, a circled set, a squared set, a parenthesized set. Map your letters onto them and you get the spaced-out 'aesthetic' look or bubble letters.
Two reasons. First, the app's font might not include a glyph for a particular character — so it draws the 'missing glyph' box (the little rectangle). Second, the app might deliberately reject certain Unicode ranges in fields like usernames, for moderation or layout reasons. Neither is something a generator can fix. The practical workaround is to pick a style built from the most common characters — Bold, Small Caps, and Full-width are the safest bets across the most apps.
For a bio, a caption, a game name, a one-line joke — it's fine. For long passages or anything that matters for accessibility, it's a real problem: many screen readers announce these characters individually ('mathematical bold small a, mathematical bold small b...'), and search engines see gibberish, not styled text. So: short and intentional, yes. Your whole 'about me' paragraph or a web page heading, no — use real formatting there.