Discuss why play is so crucial to the development of a child. What are the possible outcomes for a person who does not learn to play as a child?

According to Psychology Today, play can be identified or defined using the following five points: first, it is what the child chooses to do: it is a desired, self-directed activity that is not imposed on the child. Second, it is performed for itself, not to achieve an end: the journey or activity of play is its own reward. Third, those engaged in the activity of play generate the rules for play. Fourth, play is imaginative and fictive, and those engaged in it are aware that it is fantasy. Even a child as young as two can learn the difference between fantasy and reality. Finally, play involves an active, not a passive, state of mind that engages the child in a non-stressful way.
The benefits of play have been well documented. Play is crucial to the development of the child for the following reasons:
It develops creativity and imaginative skills in children and is vital to brain development. On an individual level, children from a very early age process and interact with their world through play, which allows them to imitate and practice adult skills and behavior, overcome fears, and gain a sense of mastery. This, in turn, leads to self-confident and resilient behavior. It helps children learn and explore what their interests and passions are and gives them scope to begin to develop them.
On a social level, play with other children teaches such skills as working in groups, sharing, bargaining, and standing up for themselves. Children left to manage their own play with minimal adult intervention can develop important leadership and community-building skills.
Finally, play tends to be active, engaging the body. Therefore, it correlated with physical health.
Play is so important that the United Nations High Commission for Human Rights has named it as a right of every child. (Office of the United Nations High Commissioner for Human Rights. Convention on the Rights of the Child. General Assembly Resolution 44/25 of 20 November 1989.)
Possible outcomes for a child who does not learn to play, such as children who are forced into child labor or those who are over-programmed with organized activities can be stress, anxiety, and depression. Further, such children are at risk of not learning to be independent, to think creatively, or to discover how to solve problems. Play deprivation is linked to poor resiliency in adulthood, addictive behavior, reduced ability to self-regulate, and reduced ability to achieve mature human relationships. Criminality is also associated with a lack of childhood play.
Even before adulthood, however, the negative impacts of a lack of play can appear. For example, children who have been deprived of play as toddlers can enter school not knowing how to play and therefore may engage in more aggressive behavior towards other children, leading to a lifetime pattern of poor socialization. For every benefit of play listed above, the negative correlative applies to a child deprived of play: for instance, if play helps a child learn to share and develops a healthy physical body, lack of play means the value of sharing is not developed, and the child may be likely to be physically weaker or overweight.
Play seems like such a simple thing, but it is increasingly being curtailed among children, even in affluent environments. It is crucial, however, for the psychological health of children and for their successful socialization into the larger human communication.
This should be a help to get you started; you could especially look at the references in the articles cited to find out more.
https://pediatrics.aappublications.org/content/119/1/182

https://www.psychologytoday.com/us/blog/freedom-learn/200811/the-value-play-i-the-definition-play-gives-insights