Here you go, I'll share my personal list of free ressources and assets :
Textures:
Different types of ressources / assets:
- Quixel Megascans (textures and assets)
- Free 3D (models)
- PolyHaven (game assets)
- World Machine (terrain generation)
- Glitch game art (CC0)
Thanks for AmbientCg, I didn't know this one. Even though Quixel was bought quite recently by Epic Games, their assets are still usable with Unity.