This has to do with the age of the post and is in fact happening by design. When it was created in December 2018, Stack Exchange didn't support ``` code fences. It did, however, support ``` as a way of entering inline code with like breaks. That's what the answer in question was doing, purely by accident.
In January 2019, we added support for code blocks ...
I usually double-up the indent for each level of bullet point you're under. So here that's an indent of 8 spaces. And it previews correctly.
1. Update your `/etc/default/grub` accordingly:
Update your /etc/default/grub accordingly:...
I solved it by indenting the code block by four spaces, which subordinates it under the ordered list:
1. update your `/etc/default/grub` accordingly:
The issue of the Preview showing something different than the post in the end of ...