I just tried this and when I tried to glue two sheets that were not immediately adjacent the glue option didn’t appear, but when they were one on top of the next, and I selected both, the option was there.
@dfay I just checked—you are correct! Thanks for solving the mystery. I knew I’d been able to glue sheets before. After reading your reply I realized that I was trying to glue two sheets separated by a folder (chapter division). I was hoping to glue them together to get a better feel of the flow of my transition between chapters.