It seems like you can no longer hook into the GameMenuButtonLogout button like this:

3x FlashTaskBar/FlashTaskBar.lua:355: attempt to index global 'GameMenuButtonLogout' (a nil value)
[string "=[C]"]: in function `xpcall'
[string "@FlashTaskBar/libs/DF/addon.lua"]:169: in function <FlashTaskBar/libs/DF/addon.lua:129>

I saw this PR on ACP, maybe it can help with how to hook this button as well: https://github.com/Legacy-of-Sylvanaar/addon-control-panel/pull/6/files