Products can be filtered on the Product page by going to Products > Products, and clicking on the Filter button to the right of the Search box. In addition to filtering by Product Title, UPC, or SKU, you can also filter your products by Category, Department, Vendor, Manufacturer, Availability, Images (if a product has or doesn't have them), Digital Download, Kit, Serialized inventory, Product Status (Active, Deactivated, or Deleted), In Stock, Items with $0 Price, and Date Created.
For Category, Department, Vendor, and Manufacturer filters, you can set it to filter to None Assigned, so you can find products that have not yet been set up for those areas.
Once you have selected your Filters, click Search at the bottom, or if you need to start over, you can click the Reset button. Once you initiate the Filter search, you'll see the products that fit your Filters and you can work with them as needed. If you need to clear the current Filter search, you can click the X next to the Filter button and it will clear them for you.
Note, deleted products can be restored by sorting the 'Product Status' and filtering for Deleted products, finding the one you want, and then clicking on it to open it. Once you Save the product at the bottom, it will be Active again.