I use italics for the rare emphasis, internal thought, or quote.
I used the blockquote a couple of times to show a literal quote or to show author's note. In short, to make it stand out.
For example, here:
https://tapas.io/episode/1758171
It's an excerpt from a book in this fantasy universe.
Be careful with bold. It's not very professional in fiction. Maybe if you have scene markers it could come in handy, although that's not really needed on Tapas since readers like short chapters anyway.
I used the headings and bold in my trivia episode since it's no longer the narrative, more like an article. I expect some readers to skim the content to see what's in it. Headings help organize. You only need that in non-ficiton.