It’s really unfortunate that Unity 6 doesn’t seem to be clearly advertised as “preview-don’t use for production”. It’s not even “Tech” (which still it would be equivalent to “beta”). I’ve got a report from an user that Unity 6 was somehow auto-downloaded by the Hub, and asked me why my vehicle physics package is not working.
Physics-wise, there are non backwards-compatible API changes, as well as show-stopper bugs still unresolved, such as this one: Wheel Colliders drop through the ground if any settings on the Rigidbody are changed in Unity 6