Why this bold survives copy and paste
Normal bold is formatting: the app stores "H" and a separate note saying "draw this heavier". Most social apps throw that note away when you paste. The letters here are different characters. ๐ is U+1D407, MATHEMATICAL BOLD CAPITAL H, a separate code point in the Unicode standard, so the bold travels with the text.
Those characters were added in Unicode 3.1 (2001) for mathematicians who need bold ๐ฏ for vectors. Social media users found them later.
Serif or sans?
Bold serif (๐๐จ๐ฅ๐) reads as classic and formal and has bold digits ๐๐๐. Bold sans (๐๐ผ๐น๐ฑ) looks closest to the heavy UI text of Instagram and TikTok, so it blends into captions best. Bold italic (๐ฉ๐๐๐ ) adds emphasis but gets tiring to read in long lines. Serif and sans bold italic have no digits, so numbers stay plain.
Use it sparingly
Screen readers such as VoiceOver and NVDA may read each styled letter by its full name or skip it, and search inside apps usually cannot match ๐๐จ๐ฅ๐ to "bold". Bold a key word or a name, not a whole paragraph.
Want every style at once? The fancy text generator casts all of them from one box, and how Unicode fonts work shows whatโs going on under the hood.