I’m having the same issue and refuse to give up on getting the URL Scheme working. Trello themselves gives us the code how it should work here: Automate with URL Scheme | Trello | Atlassian Support
Which is trello://x-callback-url/createCard?shortlink={board_shortlink}&name=MyCardName&description=MyCardDescription
I enter the shortlink and replace MyCardName with [[title]] and MyCardDescription with [[body]]. The action opens up Trello and says that it worked, but no new card has been created.
Any ideas what could be wrong?