Recently block references were added as a new, Roam-like feature to Obsidian so they could be embedded like with headers and the text below.
Headers can be collapsed (lists too), but blocks cannot, not in markdown. Today someone asked in a Discord channel if blocks can be collapsed, and Silver answered that that can only be done with HTML code, and she linked to a webpage where it is explained how to do it.
I have added the code to the repository because despite it not being markdown code, collapsing a block might be something other Obsidian users might be interested in.
Note: if one includes a link like text in the block between <details>....</details>, you have to use <a href="https://your-site.com">Some text</a> to make it a clickable link. An internal link/wikilink, however, is not rendered clickable. Just something to bear in mind. 
You can find it in the file under the HTML header, and I have called it Disclosure widget for a block of text.
You can copy/download the code from Github.