HOW DO I COMPLETE MY PROJECT IF FINAL CUT PRO IS SAYING 'CANNOT SAVE CHANGES TO “UNTITLED FILE"

You've run out of disk space. 10% - 15% free space is the minimum, which for a 1TB drive is ~100GB. You might try deleting the render cache to see if that frees up some space. If your project really requires that it be this large, I suggest you get a large external drive to work off of so the OS has the required free space on the internal drive to operate.

As already said, you absolutely need to clear some space.

Once you have put enough away so that FCP can at least start, and BEFORE you do any editing, select the library in the browser sidebar and do File->Delete Generated Library Files. Check all the boxes and confirm. Quit FCP and look at how much space you have. I am guessing you ard going to have maybe half of your drive free.

What Phil and Luis said! Quite a few FCPX users here have had their systems so completely borked by a "cleaning" app (CleanMyMac, we're looking at you) that it required a complete disk reformat and reinstall from scratch. Not a fun way to spend an afternoon.

Also, when you do free up enough space to launch FCPX, then delete the Generated Library files, be sure to turn off Background rendering in Preferences or FCPX will start re-rendering the cache files you just deleted, maybe filling up your drive again.

Here is a suggestion that may work. In the finder navigate to where the Untitled file is saved and duplicate it. Then rename it to something else and open the renamed file FCP.

+1

First up you might try house cleaning your hard drive a bit by backing up some stuff and then moving it off your drive and emptying the trash. The Mac operating system needs more free space than what you are working with. Final cut may be manipulating large cache files that prevent it from proceeding if you have such a small amount of free space. Also (and I don't know if you have/haven't tried it) always rename any of the FCP files in the application itself. It just makes it easier for the program and you and saves you from having to relink things.

After you have freed up a bit of space on your drive it may be prudent to reboot and then try opening your Library again. Fingers crossed :)

Just one more suggestion about making some spare space - don't be led into downloading any programs (free or otherwise) that will offer to reclaim lots of space for you. Some of them do - with the end result that your computer shows strange behavior as the 'cleaning' program has removed something that the Operating System needed. As an experiment I tried one recently after backing up my drive to several externals. Spent the rest of the afternoon restoring from the backups.