Since it's overly complicated, here's how you enable formatted toots:
1. Go to "app settings" in the web app and select "Show content-type choice when authoring toots"
2. Click the icon next to the globe to select either Markdown or HTML formatting.
3. If you want this to be permanent and also work on mobile apps like Tusky or Toot!, go to Preferences -> Profile -> Other and change "Default format for toots".
@systemf thanks lol i was entirely unable to figure it out
Also note that for instances not running glitch-soc, the fork of Mastodon that types.pl runs, users will see the raw Markdown.
Finally, if you're posting code, please put a content warning on it -- screen readers hate trying to speak code.