hrrrngh

Itch and Kenney have good ones:

https://itch.io/game-assets/free

https://kenney.nl/assets (all CC0)

Synty also has a nice placeholder pack for $7. The post-it notes are kind of adorable:

https://syntystore.com/products/polygon-prototype-pack

I don't think most of these are made for Godot, so you may have to mess around with import settings or set up tilesets/materials yourself

If he collects enough metrics, he could make a horrendously cursed blogpost out of it like Aella

Unsure if this meets even the lowest bar for this thread but I was jumpscared by Aella while browsing Reddit