Maybe this:
/run local cb = ChatFrame1EditBox cb:SetScript("OnEditFocusLost", nil) UIParent:HookScript("OnEvent", function(self, event) if event == "GLOBAL_MOUSE_UP" and cb:IsShown() and not cb:IsMouseOver() then cb:ClearFocus() end end)
You’ll have to /reload before using if you have any other script in place
If you want the EditFocusLost processing re-enabled after clicking it will require some extra code and for it to be moved to an addon (which you will probably want to do anyway if it works).