Is there any way to stop GPU work running that is scheduled using metal?
Long shader calculations don't stop when application is stopped in Xcode and continue to take up GPU time and affect the display.
Why is this functionality not available when Swift Tasks are able to be canceled?
There's no supported way for you to cancel a task while it is running on the GPU with the APIs currently available. If you'd like us to consider adding the necessary functionality, please file an enhancement request using Feedback Assistant. Once you file the request, please post the FB number here.
If you're not familiar with how to file enhancement requests, take a look at Bug Reporting: How and Why?
Perhaps if you can tell us more about your particular use case we can advise you about alternate solutions.