MacOS safe mode is used to diagnose and troubleshoot problems when your Mac doesn’t work properly. If you receive an error message "The operation can't be completed because the disk is full.", instead of backing up, wiping and reinstalling, you are recommend to boot your Mac in Safe Mode and empty Trash again.
#4 Fix Mac Trash Won’t Empty Because Disk is Full
How to Fix Mac Trash Won't Empty File in Use, Lock, Disk Full, etc.
Then Empty Trash again to check if the problem is fixed.Click on Apple menu and select Restart.Mac Trash won’t empty error may be cleared by restarting the Mac. Your Mac will become clean and fast, as good as new. When restarting Mac, this process will empty active RAM and start everything from scratch to clear faults. Confirm to Empty Trash and check if your Trash can be emptied on Mac.Then right click on the Trash bin icon and select Empty Trash.We just quit the app and get it back to default settings for a new task. Trash may stop working and freeze for a variety of internal and external factors, but quit Trash and redo Empty Trash can be an easy solution for this issue sometimes.