Wrong solution!
It might work but it's not the correct way + you will most likely get into trouble after next updates again.
LibStub is outdated and must not be used anymore!
Please delete the subfolder libs of the addon and install all libraries in there directly into your live/AddOns folder!
e.g. LibAddonMenu-2.0
And change in the code of the addon the call to LibAddonnMenu-2.0 via LibStub to the global LibAddonMenu2.
e.g. change this:
local LAM = LibStub("LibAddonMenu-2.0")
to this:
local LAM = LibAddonMenu2
You will find several posts in the forums about LAM 2.0 (LibAddonMenu) where older addons provide the libraries in the subfolder libs and call it via the addon's txt file directly. Here is an example what to do then:
https://www.esoui.com/forums/showthread.php?t=9624