If you use iCloud, then every installed app has its own container (Folder Type / Kind labeled "App Library" in Finder). If you never picked any other location, you probably have saved your files in that container as it's the default location for new or default files created inside an app. For Numbers that should be "iCloud Drive/Numbers/" . Unless you delete that folder manually, it should remain there after deleting the corresponding app. I don't think it's possible to accidentally save files in the app bundle itself, as it's protected.
From what I've read so far, the shift to Apple Creator Studio is significant. I think this hasn't been well communicated nor executed, that's why I'm still holding off and evaluating if I will stay in the Apple Ecosystem at all. This move has shattered my trust in Apple. Good luck with recovering your data, I feel you.