If a cat keeps meowing after the lights are turned off, it may be because it feels uneasy in the dark or is seeking attention. To alleviate this, try leaving a small nightlight in the room to provide a dim light source and increase its sense of security.
You can also try soothing your cat when it meows, such as by speaking softly or petting it, to distract it and relieve its anxiety. If the cat's meowing is persistent and disruptive to your rest, it is recommended to consult a veterinarian or a professional pet behavior consultant for more specific solutions.
