Is there any differences between GameObject.SetActive(false) and GameObject.transform.active = false?

The transform class has no documented property or field named active.

So, it appears that the difference is that one of these things exists and the other doesn’t.

Even if there is an undocumented transform.active, I’d recommend against using it. It’s undocumented, may not work as expected, may not exist in other Unity versions, and may not be as clear to other developers who work with you.

Calling SetActive on a GameObject is a clear and well-documented method. Go for that.

If you just want to disable a component – such as a renderer – many of them have an enabled property that you can use.