How to Animate The Child while the parent is already animated

Trying to animate the child relative to the parent animation , but the result always offset from the original placed position . Even though I Keyframed At The Same Position (By Using ALT+G) It Still Jump

Here’s the problem + Blendfile :

I saw the only one solution that didn’t work :
https://youtu.be/sUdV9qQXmVk

Also , this is not about parents and unparenting . The whole internet only gives me the “child of” constraint , which isn’t what I mean ..!

enter image description here

Update : deleting the config file WORKS ! Things is going well , the problem won’t occur anymore .. what makes the problem is still unknown .. since I have 30+ add-ons installed .
Maybe some of my configuration is messed up , maybe some addon changes the behavior , maybe I shouldn’t use Windows config to linux config .. who knows .