Hello, glad to solve your problems. According to your description, the reasons are possibly due to the local snapshot of Time Machine, the purgeable space on Mac, system glitches, disk errors, etc.
- 1. Restart your Mac.
2. Remove purgeable space. The difference means you have purgeable space on the drive, so you'd better use some reliable tools to clear it like iBoysoft DiskGeeker, which can safely and completely remove the space.
3. Use Mac Safe Mode. You can fix problems in it.
4. Erase local snapshots. Open Terminal and type tmutil listlocalsnapshots / and then type sudo tmutil deletelocalsnapshots xxx (replace xxx with the date and time that you want to delete). Finally, type for d in $(tmutil listlocalsnapshotdates | grep "-"); do sudo tmutil deletelocalsnapshots $d; done.
5. Repair the drive with the First Aid in Disk Utility.
6. Reindex Spotlight.
Also read: macOS Shows Wrong Free Space in Disk Utility/Storage
