Unable to clear system data on my MacBook Pro 13

If you have Time Machine enabled to do automatic backups to an external drive and you don't keep that drive connected all the time, then during those times when the ext drive is not connected Time Machine may create APFS snapshots of the changes that have been made to your stuff. These snapshots will be stored on the "- Data" volume of the startup drive and may appropriate many gigabytes of storage.

Time Machine APFS snapshots can be manually culled to free up storage space. You can view and manage TM snapshots using the Disk Utility app.

View APFS snapshots in Disk Utility on Mac - Apple Support

There is a down side to deleting TM snapshots, that being you lose the ability to recover any file changes that are saved in the local snapshots. These changes could potentially cover a period ranging from hours to days or more since the last TM backup to your external drive was made. If you work daily with files of great importance to you, then deleting TM snapshots is probably not a good idea.

To reduce the number of snapshots that TM creates, keep your external backup drive connected to the Mac at all times. If you cannot keep the drive connected, you can reduce TM's backup frequency from hourly to daily or weekly. To prevent TM from creating snapshots at all, you'll need to change the frequency to "Manually".

Part 1 of 2

System Data technically, has a mount point /System/Volume/Data 

With a mount point of /System , this Volume is part of the Operating System and can not be deleted - full stop

It is where your User Account (s)  was made when the computer was First Setup as New

We can point-out what may be included in this Volume

Though, how to reduce this is a long and complicated trial and error process

This process does not always prove fruitful

Part 2 of 2

The more  popular way to address this issue is to Start Over from Scratch 

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

For Apple Intel computers >>   Use Disk Utility to erase an Intel-based Mac followed by How to reinstall macOS

Always make a Time Machine Backup  before  proceeding 

It is also suggest to  Only Migrating the User Account and nothing more.

Emphasis on User Account Only

Reinstall the Needed and not the Wanted applications from the Apple Apps Store or Directly from the Developers

D.I. Johnson wrote:

If you have Time Machine enabled to do automatic backups to an external drive and you don't keep that drive connected all the time, then during those times when the ext drive is not connected Time Machine may create APFS snapshots of the changes that have been made to your stuff. These snapshots will be stored on the "- Data" volume of the startup drive and may appropriate many gigabytes of storage.

Time Machine APFS snapshots can be manually culled to free up storage space. You can view and manage TM snapshots using the Disk Utility app.

View APFS snapshots in Disk Utility on Mac - Apple Support

There is a down side to deleting TM snapshots, that being you lose the ability to recover any file changes that are saved in the local snapshots. These changes could potentially cover a period ranging from hours to days or more since the last TM backup to your external drive was made. If you work daily with files of great importance to you, then deleting TM snapshots is probably not a good idea.

To reduce the number of snapshots that TM creates, keep your external backup drive connected to the Mac at all times. If you cannot keep the drive connected, you can reduce TM's backup frequency from hourly to daily or weekly. To prevent TM from creating snapshots at all, you'll need to change the frequency to "Manually".

👍

@ D.I Johnson

Notice the Sort Order Time Stamps

Have mine set Sort by Oldest

Your at 10:30 above mine, first posting @ 10:21

Please forget the previous

Just Reload this question

Sort Oder by Oldest is now normal again

Must have been an Apple momentary hiccup

👍🏽

Or.... perhaps you were a victim of Re-Titling. 🤔

Hum, maybe ?

Good point 😎