It may not be normal for a 40-day-old kitten not to poop. Usually, kittens should have regular defecation habits. Here are some possible reasons and suggestions for kittens not pooping:

Dietary issues: Make sure the kitten Have enough water and age-appropriate food. Sometimes, a poor diet can lead to digestive problems.

Lack of exercise: Kittens may need some exercise to promote intestinal peristalsis. You can try using toys to guide it to move.

Intestinal problems: Kittens may have blockages or other problems with their intestines. If the condition persists or other unusual symptoms occur, such as vomiting, loss of appetite, etc., it is best to take it to the veterinarian.

Environmental stress: New environments or unfamiliar things may cause stress to kittens and affect their defecation. Try to provide it with a quiet and comfortable environment.