You are likely still in the wrong Library folder.
The correct Preferences folder will usually have more than 500 files, often more than a thousand files. If yours has only about 50 or less, you are still in the wrong Library.
Follow the directions to go to the Go menu, then press and release the Option key. You will see the correct Library folder appear in the list, then disappear when you release the Option key. Click on that Library while holding the Option key, and then open the Preferences folder that you find now.
If you have restarted your Mac, and are in the correct ~/Library/Preferences folder, there WILL be a com.apple.desktop.plist file (guaranteed