try set focus if inventory grid has any children:
i guess Set Focus/Keyboard Focus/User Focus is not the same as “Gamepad” Focus (with dotted lines) because if i set Focus to any button “On Hovered” its not getting interactable via gamepad but in a scroll box instantly scrolls to the button ( because i set “scroll when focus changes” to instant / animated
OR
it could be that the Child Widget (Item Slot) that gets added to the Grid gets Focus but not the Button Element inside of each Item Slot.