Allow me to upload files to my document library from the app
I wanted to be able to upload a photo from my mobile device directly into the document library. I was instead forced to launch the one drive app that I didn't have.
Bortek Industries commented
I found a potential workaround. Create a modern page with the document library you'd like to upload to as added as a web app/part. I'm able to upload files on the iOS SharePoint app by navigating to a modern page set up in this way, even though accessing the document library directly gives much fewer options.
Star D. commented
My experience mirrored the original poster's. I was trying to access a Picture Library (both via Site Contents and the link under "Recent" in the Quick Launch) and was prompted to get the OneDrive App.
Additionally, after I installed it, the OneDrive app will not open that Picture Library (the SharePoint App will, but only through Site Contents) .