If you are also facing the problem of note 9 apps keep crashing, then here are a few ways to fix this issue-

Try to clear the cache files- most of the time the reason for apps crashing is the cache files. So close all the running apps and clear the cache.
Try to update the system and apps- Go to settings > software update > check for updates. Then follow the on-screen prompts and install the update.
Try to reset the app preferences- settings > apps > more settings > reset app preferences.