Task lists (or checkboxes, tasklists) work with most characters enclosed with
[ ], not just x os space. Even emojis seem to work, with the exception of
🔁, for example. Here’s a snippet I tried in Obsidian.
- [ ] - [x] - [X] - [a] -  - [?] - [✔] - [🔁] - [❌]
Obsidian mostly supports Github Flavored Markdown, and the GFM spec supports any enclosed character.
I’m on Obsidian v0.12.15, Windows 10.