How can I accurately count total items in draft orders?

Is there any way I can count the total items reserved in draft orders?

I’ve tried many ways but it doesn’t seem to work…

The short answer is (probably) “no.”

Draft orders don’t ‘reserve’ products/inventory. They’re simply quick-links / invoices for the customer to purchase the items. Until they actually add the products to their cart and proceed to checkout, no inventory is actually deducted or reserved.