Why can’t a dog’s eyes close after death?

The reason why a dog’s eyes cannot close after death is because when alive, the eyes can open and close freely and rely on muscles to operate. Rigor mortis will appear on the corpse after death. If the dog's eyes were open when it died, then the muscles of rigor mortis will begin to contract violently after death, so the dog's eyes cannot be closed.

Are there any signs that a dog’s eyes have not closed after death?

The dog's body was in an extremely weak state before death. Perhaps the brain nerves could not control the contraction of the orbicularis oculi muscle freely, so he did not close his eyes. This is not a sign, just a normal physiological reaction. As long as you treat your dog well when you raise it, it will leave happily. So some owners should not feel uneasy and sad because the dog does not close its eyes. While the dog grows old with you, you must also grow up.
Because dogs know love better than people, their lifespan is very short.