I love excalidraw, but I have to agree. It also looks very unprofessional so if you ever have to write customer-facing diagrams, you have tool fragmentation. I just stick to draw.io now (aka diagrams.net)
Why does it cause tool fragmentation? You can change the font to a normal sans-serif font or to a monospaced font.
Personally I like the default font. It looks weird to have my crappy doodles next to a normal computer font. The default one is very legible but has a style (and ligatures) that make it feel not too neat
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.