How to disable the fast grid in searching?
Could you specify what you mean by fast grid? If you mean an ItemType searching automatically when opening the search grid, you can specify that on the ItemType itself. In the screenshot below, the Auto Search checkbox is what determines whether or not a search automatically happens upon opening the main grid for an ItemType.
Let me know if this is what you were referring to!
This is the one I'm asking about
The type ahead doesn't interfere with the users ability to select an item through the search grid (which is launched by clicking the ellipses button). Are you trying to force the use of the search grid? If so, could you elaborate on what the use case is? I'm not sure I understand the benefit to limiting the users options for data entry.
As AJ mentioned, it is possible to remove this functionality, but the time investment in figuring out how to do so would likely be significant and may not be worth it if you're only getting a small benefit.