For very basic drawing, search for "online whiteboard." I also searched "shared drawing app" and a site called Drawpile came up, which looks like it's more drawing focused rather than office whiteboard focused.
The linked thread has more information about the Drawpile, but in short the Drawpile is a drawing application allowing for real time online drawing collaborations on a shared canvas
https://drawpile.net/
Drawpile.
It's free, you can join online drawing rooms and it's dead simple. Also has touch-based undo/redo buttons so you don't need a keyboard as much.
My only complaint is that it creates a canvas as soon as it opens, and if you want a larger one you need to tell it to.