This works in the raw markdown edit mode, but in preview mode, if I write this:

<details> <summary>People</summary> [ ] Bob [ ] Alice [x] Nemosaltat </details>

Preview mode will yield this (all on one-line):

[ ] Bob [ ] Alice [x] Nemosaltat

It’s collapsible, but not visually pleasing for longer lists.

My solution has been to do this:

<details> <summary>People</summary> [ ] Bob <br /> [ ] Alice <br /> [x] Nemosaltat <br /> </details>

But it’s less pleasing to look at in edit mode, and I have to remember to append the break tags.