I'm not sure if same situation, but I ran in to similar issue why using Sonoma Beta. I've had the "Move to...." icon in my toolbar in Mail for ever. Then after an update it had become a single unnamed folder icon that served as a drop down with no suggestion for a folder. I thought it was gone. However when I went in to customize toolbar, there are now TWO icons called move. My original Move to.. had become its own new menu bar icon while the original was now defaulting to the forced dropdown pick view. I hope that helps someone having a similar issue.