We'd need to see the actual terms of that special to be sure, but generally % off only applies to Buy It Now, not auctions or offers.
ETA: Click on See details under the coupon code box: https://www.ebay.com/e/daily-deals/23-rw35-labor-day-sfc-main
It refers to "purchases" and only applies to the items in the search results on the same page BELOW the offer (not every eBay item or what come up in the usual search box at the top of the page). All the ones I am seeing are Buy It Now only.
