If you’re working with Numbers and don’t want to store them on iCloud, you can store them directly to OneDrive. This is handy if you have extra cloud storage from Microsoft, such as the 1TB included with a Microsoft 365 subscription.
To do this, open the Settings app on your iOS device and tap Numbers. Then, tap Document Storage and select OneDrive.
Dropbox, Box, and other third-party cloud storage services are not supported on iOS. As a long-time Apple user, I want to point out that Apple has a history of removing features like this at their discretion. Remember when you could sign up for social media accounts directly from your iOS settings? Facebook, Twitter (RIP), and Instagram. It was like using social media for the first time in the mIRC era. Those were the days.
Don’t be too happy that Apple allows direct connection, and don’t despair if your favorite cloud storage wasn’t the chosen one. Nothing lasts forever!