So I built gp-treemap, a canvas-based web component that renders GP-style treemaps with millions of nodes: https://github.com/imbue-ai/gp-treemap/
If you want to give it a spin, try something like this command to visualize hierarchical disk usage:
npx -p @imbue-ai/gp-treemap gpdu ~/Downloads
Fun fact: I built gp-treemap as a test case for Imbue's Sculptor (https://imbue.com/sculptor/) and Blueprint (https://imbue.com/product/blueprint) tools.