It's not on a whiteboard, nor was it written by hand. It's a computer font.

The Excalidraw website describes itself as: Excalidraw is a virtual collaborative whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them.

And the GitHub repo says: An open source virtual hand-drawn style whiteboard. Collaborative and end-to-end encrypted.

It's the intended design...

Cool. I have stated my opinions on their intended design.

Cool. I have stated the facts of the product.

It just looks weird not childish.