Hello Jette,
You don't need to uninstall AD, here's how to do it if you're running Windows, I guess the procedure is similar for Mac:
Hold down the Windows key on the keyboard and press the R key. In the window that opens, type:
%AppData%/Affinity/Designer/1.0/
click on "OK", open the "Temp" folder and delete its contents.
If Designer does not close, use the task manager to close it, then delete the "Temp" folder, the next closing will be done normally.
I hope this will help you.
I also give you one of the links to this topic on the Affinity forum:
https://forum.affinity.serif.com/index.php?/topic/71247-designer-will-not-close-saying-1-document-loading/&tab=comments#comment-370123I hope this will help you.