This app was mentioned in 4 comments, with an average of 1.00 upvote
It's this one:
https://play.google.com/store/apps/details?id=com.symcoding.widget.stickynotes&hl=en
It's actually not that great, you can only draw in one color in one line thickness and you have to pay for extras. And no, you can't draw straight on the widget, you have to tap it first and then draw in the app. I use it because it's the fastest one out there - tapping on the widget loads the app where I can draw instantly, like it was already loaded in memory.
Here's the one I use!
https://play.google.com/store/apps/details?id=com.symcoding.widget.stickynotes
So I unchecked the default sticky notes in Today view and added another widget I downloaded that's working good. https://play.google.com/store/apps/details?id=com.symcoding.widget.stickynotes