If you are a student using a device with MacOS and you have issues with submitting a Turnitin assignment because Turnitin gets stuck on "Uploading..." while using the Safari browser, the best solution at the moment is to use a different browser to submit your assignment (Google Chrome, Mozilla Firefox, etc...).
Turnitin will take a 5 hour maintenance window on April 20 from 9:00 AM CDT to 2:00 PM CDT. During the downtime, you will not be able to utilize the Turnitin Tool, including Turnitin assignment submissions, processing and grading, in Blackboard Learn.