Can I prevent users uploading into OneDrive from mobile app?

Hey Deleted 

I'm unaware of a solution to what you need; most of the settings are concerned with users egressing data out of OneDrive rather than stopping data going into it. 

A poor workaround (if you can call it that) is to set up a custom alert for any file uploaded to OneDrive outside of your corperate IP range so you are notified if someone does, but I can imagine this would get very unwieldy quickly if you have to do this for more than a handful of people.

It may also be possible to create a Flow so that uploaded files outside of the corp IP have a custom action to them - maybe some kind of approval? A heavily modified flow like this one:

https://unitedkingdom.flow.microsoft.com/en-us/galleries/public/templates/310e30cf00a34855af793fcf2749dfd5/request-my-manager%E2%80%99s-approval-for-the-selected-file/

Possibly set up for auto-reject? I'm not much of a Flow person, but that might provide a solution, though it'll take a bit of effort to get it up and running.