eBay used to close out listings after they sold but last year they made a change where all listings are now "Good Till Cancelled".
This means they stay up on eBay even when sold out.
The thinking is that you may want to add stock later, but for those that sell mostly one-offs it is an annoyance.
What you can do is go to https://joelister.com/ebay-listings and put listings in reverse order by quantity (to show all the zero quantity eBay listings).
Then select all of the zero quantity listings and pick Delist in the bulk menu on the top right.