Sep 30 2021 01:39 AM
It doesn't seem missing, the "Reuse Slides" pane is not refreshing properly.
While the pane was all grey, hovering the mouse over various sections of it, the mouse changed to the hand and the typing cursors. In one instance, I could - blindly - click on the "Browse" button, which opened the browse window. But after selecting the presentation, it just went back to grey. As I said, it seems like a refresh issue.