I tried Rigify and I found a very strange issue. After I painted full chest bone weight on body vertices, they are still affected by the neck bone somehow. I googled hard but it looks like nobody has a same problem like I have.
Would you like to help me to figure it out please?
https://drive.google.com/file/d/1KwnOk5825HrOVAxbsHc8u-_rvUQxoFQ_/view?usp=sharing
Neck joint: