Copy the iframe code from the post above. Open TextEdit on macOS. Paste the text. Make sure the document is “Make Plain Text”. Then copy the body of that plain text and paste it into an Obsidian Note. It will work.
Could do similar with BBEdit, or Notepad, or TextSoap, etc.
(Either in the post above, or just because Discourse sometimes propagates gremlins, text sometimes needs cleaning.)