Hi there, ladlidesignsaust.
The option to delete a product and services in QuickBooks Online isn't available. You can only make them inactive. This way, it will be removed on your Products and Services list.
Once the product is already inactive, it will not be deleted from the invoice you've created. However, it shows as "Name of the inactive product or service (deleted)" in transactions. And, will no longer show in reports.
For additional information, you can click this article: Remove or merge a product or service. This also provides steps on how you can make a product or service inactive and reactivate it again.
Please check this article on how to manually adjust an item's quantity without recording a purchase or sale, to match what you actually have in stock: Adjust inventory quantity on hand in QuickBooks Online.
Let me know if you need additional details, I'm always right here to help. Thank you and stay safe!