Everyone should fill out this form and ask that Apple allow users to turn off the optical image stabilization (OIS) if needed.

Apple iPhone feedback to disable OIS

And how exactly would you suggest Apple implement such a feature since OIS is a mechanical hardware? Its not software based so its not as easy as just turning it on or off. The only way would be to put the brakes on the mechanical piece with a mechanical brake. Not so simple.

Having looked at this issue at length before getting an OSMO Mobile, it's clear that as others have said there are 2 kinds of OIS - software (cinematic stabilisation) which can be (and is) disabled through a number of apps. And the hardware OIS which is mechanical and built into the camera module. Whilst to disable this wouldn't be impossible, the reality would be that it wouldn't be a priority, it would be seen as a reduction in functionality for most for a benefit for a small part of the population.   I feel that as with many cutting edge technology we as users have to manage our expectations (whilst continuing to push for perfection), in most cases there have to be trade offs.

Looking at much of the footage produced with the OSMO Mobile, it is great.  Perhaps where we should focus is encouraging DJI and 3rd party app providers to push the functionality envelope to unlock the potential of the smartphone/Osmo combo.  If I'm critical of my own outputs from the device it's 99% caused by the user/app interface, which of course means it's the app ;-)