The same indent that works under a dash flattens a numbered list and renumbers it. Here is the rule that decides.
It compares your child's indent against one number: the column where the parent item's own text begins. Everything else follows from that.
A dash plus its space is two columns wide, so a child nests at two. Write 1 dot space and the floor moves to three.
Two spaces under a numbered item makes the child a sibling. Ordered lists number by position, so your 1 is published as 2.
Each marker gets a four-wide window. A dash nests at two through five spaces. Six is already too far.
An indented code block cannot interrupt a paragraph, so the over-indented line joins the parent's text and the dash prints literally.
Items 1 to 9 need three spaces, item 10 needs four. Indent everything by three and only the bottom of the list collapses.
Four clears every common marker and stays under every ceiling. Verified in markdown-it, marked and micromark, four levels deep.
Indent to the parent's content column, and stop before four past it.