This hides the Banner GUI Popup and Mutes the achievement sound
Type in chat
/run AlertFrame:UnregisterEvent(“ACHIEVEMENT_EARNED”)
/run MuteSoundFile(569143)
to reverse this or undo this effect you can type
/run AlertFrame:RegisterEvent(“ACHIEVEMENT_EARNED”)
/run UnmuteSoundFile(569143)
You can also right click the General Tab in chat, Settings, and Uncheck Guild Announcements if you don’t want to see that either.