If you're wondering why some posts have got rich text formatting like bold, underlining, italic etc, it's because many customised Mastodon and non-Mastodon servers include support for creating rich text.
Standard Mastodon servers can show rich text, but cannot create it. You can move your account to a server that supports rich text creation if you want to make such posts yourself.
More info about rich text on Mastodon and the Fediverse at:
➡️ https://fedi.tips/is-mastodon-compatible-with-rich-text-formatting-such-as-markdown
