Bold Text Generator
The bold above is not a bold button. It is the Mathematical Bold alphabet, a separate run of Unicode characters that are drawn heavy, so the weight travels with the text instead of with the page.
These are characters, not formatting, which is why they survive a paste into a bio. It is also why a screen reader will not read them as ordinary letters, and why some sites refuse them in a name field.
One of the few complete sets
Capitals start at U+1D400, lowercase at U+1D41A, digits at U+1D7CE. Every letter in both cases exists, and so does every digit, with nothing patched in from another block. That makes bold the safest style here: a word never comes back with one plain letter stranded in the middle of it, which is exactly what happens with cursive. The digits matter more than they sound. A year, a price or a phone number converts as well, and most styles cannot do that – italic and script have no numerals at all, so numbers stay plain.
There are two bolds
The row above is the serif one. Unicode also has a sans-serif bold at U+1D5D4, and since almost every phone interface is set in a sans-serif face, the sans version usually sits more naturally in a bio and stays legible at small sizes. Compare the two before you paste: sans bold is the same idea from a different range.
What it costs
A screen reader announces each character by name, so a bold word is read out as MATHEMATICAL BOLD CAPITAL A and the rest of its family rather than as the word. Keep it decorative. Beyond that: a search for the plain word will not match the bold one; some platforms refuse these characters in name fields; and when a device lacks the range the fallback is an empty box, not a plain letter. Accented characters have no bold form, so they pass through untouched.
The other styles, and the block each one comes from, are listed on the main styles page.