Hello richierio1985,
Thank you for using Apple Support Communities!
It is my understanding from your post that when you open a new document for Keynote and Pages that the apps quit unexpectedly. I recommend testing the issue while your Mac is in safe mode and/or in a new user account. The following articles have the steps you will need to test the issue in both safe mode and in a new user account:
How to use safe mode on your Mac - Apple Support
"Safe mode prevents your Mac from loading certain software as it starts up, including login items, system extensions not required by macOS, and fonts not installed by macOS. It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. And it deletes some system caches, including font caches and the kernel cache, which are automatically created again as needed."
How to test an issue in another user account on your Mac - Apple Support
"If an issue stops happening when you log out of your macOS user account and log in with another, the issue could be related to the files or settings in your user account."
Best Regards.