Can't assign a keyframe on custom properties as an action type

[gor-rot]

When I want to assign a keyframe to animate an action, it's supposed to be in an action, but instead, the keyframe is on a rig. So when I change action, the keyframe is not changed with it.

[Mustard2]

Hi! This might be a problem of how the IK/FK button has been implemented in the rig and in MustardUI.
Can you please send me the file (Stripped with textures, just the bare minimum to debug).

[gor-rot]

Hello! Here are the files. I provided Rigify and AutoRigPro in this link.
https://drive.google.com/file/d/1IjyDYtaVoDw05yvLVphifsNOO8FifAPI/view?usp=sharing
Thank you.