This version has been compiled with Java 16 and will most likely not work with older versions of Java. I recommend you to update as soon as possible. You can find more information on how to do that on PaperMC wiki: Java 16, MC 1.17, and Paper - Announcements - PaperMC Forums
Changed HideButtonsOnSinglePage config option to AlwaysShowPageButtons.
If set to true - it will displays Next and Previous page buttons at all times, in other case - buttons will only be displayed if there's a Previous or Next page.
Did some major code refactoring, which should increase the performance ever so slightly.