System data
Why does the system data has used 466GB of my Mac?
MacBook Pro 13″, macOS 12.6
Exactly how many upGrades has this computer experienced in the life-time of this machine.
Example: computer originally came with, say macOS High Sierra macOS 10.13 when Brand New. It was upGraded to Mojave. Then upGraded to Catalina and so on and so forth until it was upGraded to Monterey
That would be 6 upGrades in the life-time of this computer
The accumulated effects of 6 upGrades and third party software installed and uninstalled would eventually present this question you have asked.
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Notation - If the user is using a cloning software like Carbon Copy Cloner - suggest tweaking the Safety Net Feature in this software. It may be making additional Snap Shots that are not being Cloned to the Eternal Drive. If this should be the case, these Snap Shot could be using additional space on the drive
The final word from Apple on Managing the " Other/ System Data “ Category
Other / System Data: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.