Is ghusl obligatory and must prayers be made up due to the discharge of a fluid that is possibly semen, as a result of reading arousing material, noting that ghusl was performed later due to a wet dream?

You should avoid reading provocative materials and repent for what has passed. If you are not certain that anything was discharged, then neither ghusl nor anything else is required of you. If you are certain that something was discharged but doubt whether it is manī or madhī, you may consider it whichever you wish. If you consider it manī, ghusl becomes obligatory. If you consider it madhī, wudu’ becomes obligatory. If you are certain it is manī and you experienced pleasure and then relaxation after its discharge, ghusl becomes obligatory, as well as making up any missed prayers if you had not already performed ghusl.