It is normal for an 11 year old to go through different emotions and moods, as they explore and transition in life. Crying is one of the ways a person expresses their emotions, and it is completely normal.
It may be hard to understand why your son is crying, but the best way to approach this is to validate the emotions he is feeling. Talk to him about why he might be feeling this way, and help him to express his feelings in a healthy manner.
It is important to try and figure out what might be causing the tears, such as any underlying stresses, anxieties, recent changes, etc. Understanding these emotions can also help him to manage and cope in a healthy way, with the support of adults in his life.
Additionally, helping him to build self-esteem and incorporate activities that make him feel good about himself can also help in reducing his tears. It is important to remember that some days might be more difficult than others, but that it is okay to cry and feel emotions, and you will be there to support him.