What is the ruling on lying to the manager at work regarding an absent colleague, knowing that the work environment lacks commitment, and lying is considered a courtesy to colleagues to avoid being described as not keeping a secret or lacking trustworthiness?

The default is that lying is forbidden, based on the decisive evidence that supports it. What was mentioned in the question does not constitute a necessity or an urgent need that would permit lying. Fear of not being loved by people does not justify lying, because the hearts of people are in the hand of Allah. A person should prioritize pleasing Allah while dealing kindly with people, and repent to Allah for what they have done.