Keynote for mac not opening documents

Hello everyone.

I have encountered a new issue on my mac where when I try to open a document from keynote on my mac, I get a pop-up saying: Keynote could not open <filename>.key. The file I am trying to open is from my iCloud keynote folder, and I have tried to open other iCloud keynote projects too. I think the problem may be related to an update I'm trying to install - the update has downloaded but it is not installing. It just keeps "waiting to install". Ideally, I would like to know why I can't open the document, but if somebody can help me figure out why the update is not installing, I can see if the new version fixes my original problem.

Thanks all.