Both Unity & DOTS/ECS Packages are undergoing rapid changes.
Please use exactly the recommended Unity version & Packages:
Unity: 2020.3 LTS (!)
Burst: 1.6.0
Entities: 0.17.0
Unity.Physics 0.6.0
HybridRenderer 0.11.0
DOTS.Editor 0.12.0
Do not upgrade yourself. DOTS is in preview, newer versions always break something. Let me worry about this for you, only update when I update 😉To get started, import DOTSNET from the Asset Store, open one of the example scenes & press Play!