If you use Apple Notes on a Mac, you might enjoy ProNotes.

It’s an little app that can watch what you type in Apple Notes and on certain triggers, such as ### or [] it converts your text to Apple Note’s formatting:

Animated Gif that shows how ProNotes expands two hash symbols to a second level heading, and two brackets to a task checbox

I miss a couple more options that could be auto-expanded, such as > for block quotes, ``` for code blocks and single backticks for inline code. Maybe future updates will bring those.

Beyond keystroke expansion, ProNotes also provides a medium-style floating formatting toolbar, that appears any time you select text:

I like that every feature can be turned off. I really don't need any more menu bar items and I can imagine the floating toolbar become annoying soon. Here you can see the apps current settings:

ProNotes settings panel

It's free (as-in-beer) and can be downloaded here:

Supercharged Apple Notes