1
Your screenshot seems to indicate that is Adobe software like Photoshop producing that error, is that correct?
If so, it is best to remove the scratch disk from the C drive and use another drive on your PC that has plenty of space for the Adobe Scratch Disk.
Open Photoshop.
Go to Edit - Preferences - Scratch Disks.
In there, you can disable the Scratch Disk on the C drive and set it up on the D drive.
2
For the space on the C drive problem.
Download the free TreeSize app from the Microsoft Store.
Very Important - to run TreeSize, you must right click its icon and choose Run as Administrator.
Please provide a screenshot of your C drive in that TreeSize utility, so I can see your hard drive and work out where that space is being used and if there is an underlying problem.
Please ensure the full TreeSize window is in the screenshot, there is information on the top and bottom bars I needs to see.