Read entities inventory:
Must be done in command block. To trigger redstone or another commandblock, you must set the main commmandblocks’ setttings to Always Active On, and set the command block type to repeat, then place a comparator to get redstone output
/execute if entity !!SELECTOR!![nbt={Inventory:[{id:"!!ITEM_ID!!",tag:{display:{Name:'{"text":"!!Item_Display_Name!!"}'}}}]}]