The flow of pasting such strings is not great either. Previously you could paste a string with backticks and it would be formatted correctly on send.
Now the behaviour is to ask you every time to apply formatting. There is an option for "don't ask again" which I tried assuming it would make autoformatting the default, but it turns off the behaviour completely with no way to get it back!
Only if you care about that level of specificity of the results; and given that non-technical people love pasting code snippets into slack without the code fences, I'm guessing this change isn't even wanted by non-technical people, and only made detail-oriented folks upset
You don't need the key combo, just as you said, you just need another line, with text or a blank line. I guess before now you could but them right back-to-back? This has never been my use case, but if it was, I can see how this is annoying.