Hi, sorry you ran into this!
Because of how Apple phases out support for older macOS versions, Papyrus Author eventually stops working on them as well. Here’s more info on this topic: 10.08a Incompatible with macOS Sierra (10.12.6)
If you’ve got another computer (macOS or Windows), you can move your projects over, continue there, or export them to Word files. I can help with that as well. 
Here’s a video on moving from Papyrus Author to Word: Word Documents II: Exporting Papyrus Documents to Word
You’ll find the projects in your “Documents” folder under “Papyrus Author Documents”.
I’ve also reached out with a private message to make sure you’ll get to continue your work–we’ll figure it out! 
