Part 1 of 2
Before trying to reduce System Data, I would first check how much storage the Mac actually has and how much is being used and available.
Go to Apple menu > System Settings > General > Storage > All Volumes and note those figures.
Apple explains that available storage can include space macOS can reclaim when needed, so the System Data figure is not necessarily the same as storage that is permanently unavailable. Apple: See used and available storage space on your Mac
This is especially important because you are seeing System Data go from about 22 GB to 58 GB and then back again.
Check the available-space figure at the same time.
If System Data increases by roughly 36 GB and available space falls by a similar amount, that indicates a corresponding change in storage usage.
Get detailed information about a disk in Disk Utility on Mac
“ Amount of space available, which can include both free space and “purgeable space”—or space that macOS can free up when needed by removing files from your computer (you can’t manually remove the files that are designated purgeable, but macOS removes them as space is required) “
If available space changes very little, the System Data figure alone does not represent an equivalent loss of usable storage.
Apple describes System Data as a general category that can include caches, logs, virtual-memory files, temporary files, application-support files and other system resources. Its size can change, and macOS manages the category. Apple: Change Storage settings on Mac
So, there is not an Apple-defined requirement for System Data to return to the approximately 11 GB you had before the update.
I also would not delete things from ~/Library simply to try to bring the number down.
If the Mac is genuinely running short of available storage, starting in Safe Mode is a reasonable Apple-supported diagnostic step because macOS clears certain system caches.
It may change the amount of storage being used, but it is not a way of permanently setting System Data to a particular size. Apple: Free up storage space on Mac
If you use Time Machine, local snapshots are another thing to be aware of.
Apple says a snapshot can be created before a macOS update, but the space used by local snapshots is counted as available storage and macOS removes snapshots automatically as space is needed. Apple: About Time Machine local snapshots
I would also leave third-party “System Data cleaner” apps alone, full stop
First establish whether the 22–58 GB fluctuation is actually reducing your available storage and, if it is, what is accounting for it.
Since you are already waited nearly two weeks, I would not simply keep waiting for the figure to return to 11 GB.
The most useful next step is to record the drive capacity, used space, available space and System Data when it is around 22 GB and again when it reaches 58 GB.
That will tell us whether there is actually a storage problem that needs to be addressed.
Part 2 of 2
System Data taking up a large amount of storage is a common question on Mac. There is no single setting that simply “clears” System Data because this category can include a variety of files, including caches, logs, temporary files, and APFS snapshots.
If you want the most comprehensive solution, back up first, erase the Mac, and reinstall macOS.
For Apple silicon Macs, use Erase All Content and Settings. This removes your data, settings, and applications while leaving the currently installed version of macOS in place.
Make a current Time Machine backup before erasing anything. Apple: Back up your Mac with Time Machine
Afterward, use Migration Assistant to transfer your user account rather than the entire old system, and reinstall only the applications you actually need.
If you do not want to erase the Mac, first determine what is actually consuming the space. DaisyDisk can provide a clearer view of storage usage, and Apple documents how to view APFS snapshots in Disk Utility.
The following Apple Community discussions document additional approaches. Results can vary depending on what is responsible for the storage usage:
Also consider moving large personal files—particularly Photos, videos, music, and other files you control—to an external SSD. This is often a more appropriate way to free internal storage than attempting to delete files that macOS manages as System Data.
