System Data over 1 TB – How to slim down?

One of the few accurate reporting areas in macOS is Disk Utilities

Most of the Other Reporting methods ( space Used versus Free ) depend on Spotlight which is good for finding files, application etc

Not so good for actual Spaced Used

System Data is a collection of everything Spotlight can not needly categorize into known categories

As for managing System Data ?

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.

There is Purgeable Space and there is Empty Space.

They are not one and the same thing.

Purgeable Space which is Controlled by the Operating System. When the Operating Systems decides the computer needs additional Empty Space, it will move a portion of the Purgeable to Empty space

AFAIK - there is no User Actions to hasten this transition from Purgeable to Empty Space

It can day or longer before this will occur.

You may consider from the follow links

View APFS snapshots in Disk Utility on Mac

Locate backups of your iPhone, iPad, and iPod touch - Apple Support

If there a Suite of Adobe Applications  used on this computer ?

They may create some very large cache files that can be removed. Though, the Adobe cache files will be recreated as the Applications needs them.

https://helpx.adobe.com/ca/premiere-pro/kb/clear-cache.html

The same clearing of System Cache files can be achieved by booting into Safe Mode

They will be recreated as the System Requires 

wintifrosch wrote:

You tell me …

this is a flaw in the process of migrating TimeMachine Backups to new Hardware, and …

2. there is no way to slim down System Data but by wiping my SSD and start from scratch, without using my TimeMachine backup?

Yes, there is a way to " Start over from Scratch "

Apple makes this process as easy and doing the same thing as doing it from iPhones and iPads

For Apple Silicon computer >> Use Disk Utility to erase a Mac with Apple silicon.

Using Erase All Content and Setting will Not Touch the Operating System .

The operating system itself will remain interacted

I usually suggest that if you what to Migrate from a recent TM Backup

To Only Migrate your User Account and Nothing More during the Initial Setup Assist process

Follow on after looking closely at one of your images

These are of interest and ones I can clearing understand,

Though I do not read the language they are written in

Right there and combined account for about 174 GB of Space

Apple Silicon M1 MBP from 2021 right.

How many upGrades ( as in moving from say macOS 12 Monterey ) to macOS 15 Sequoia has this machine experienced in its short life time. ?

It is possible, the System Data Volume, has grown over each newer version of macOS that has been installed ?

Have there been Other User Account( s ), other than your current Admin Account, ever been or been removed from the computer ?

Removing a User Account and not deleting the User Account Folder during this process could account for portions of System Data issue ??