The best and the easiest solution for Your startup disk is almost full error is to clean up the hard disk. Mac OS requires to have at least 10 percent of the disk space to be left free, so all the processes can run as supposed to, so these errors and warnings shouldn't be ignored. The problem might be related to the fact that too many files are occupying the hard drive, so the lack of space is indicated with Your startup disk is almost full error until it reaches the extreme state when the system suddenly crashes or cannot work properly. Your startup disk is almost full macOS error can often occur after the new release of the OS and, in such cases, the message is not related to hardware or software issues. These messages can appear on the screen out of nowhere, or when you reboot the machine, try to run a program or install a new tool.
The error itself mainly means that your device is running out of space on the primary disk drive, and it is not good news since that can affect various processes and the performance of applications, the computer itself.
Your startup disk is almost full error is probably the issue that every macOS user encounters at least once because it is a common problem that drives people crazy. To repair damaged system, you have to purchase the licensed version of Reimage Reimage.