Cannot rename Animator Parameter

you could double click it to rename:

This is a bug in Unity 2020.1.0b3.3385

IndexOutOfRangeException: Index was outside the bounds of the array. (wrapper stelemref) System.Object.virt_stelemref_class_small_idepth(intptr,object)

After experimenting with the bug I found that the last change made before saving the project will always be reverted by Unity (because it's out of range) so if you make two parameters, rename the first and then save the project you can call your parameters what you want, instead of New Whatever. You can then delete the useless ones and the behaviour list will not rename them when selecting them.

For anyone that needs a quick solution I found that creating the parameter and then saving the project and reopening unity allowed me to then rename it.,Doubt you're gonna still need this answer but for anyone else with this problem I found that creating the parameter and then saving the project and reopening unity allowed me to then rename it.