If we can't sin in heaven then free will is not needed
The existence of suffering on Earth, despite the absence of suffering in heaven, suggests that free will is not the sole cause of evil, and a genuine relationship with God can exist without suffering.
The argument that free will is the cause of evil and that free will is also necessary for a relationship with God assumes that suffering is an inherent part of free will however, the existence of heaven, which is a place where there's no suffering challenges this logic because If a relationship with God can exist in heaven without suffering, it shows that a there are other mechanisms or conditions under which a genuine relationship can be maintained without the presence of evil. This suggests that free will, while important, may not be the only factor contributing to the existence of evil, and alternative explanations or conditions could allow for a meaningful connection with God without suffering.