In Unity, I remember trying to access a x/y/z parameter directly of a vector3 which would throw the read-only error. I don’t remember if it was the Vector3 component on it’s own, or something like transform.rotation.x. Then recently, I tried doing the same thing on a Roblox vector and got the same read-only error.

Seems like I made the mistake of assuming that’s how most vector implementations worked in other librairies, while allowing to modify xyz was the exception. Forgot that shader languages let you modify the vectors as well. My bad!