more than 100GB space in “syatem data”

Most of the System Data is probably Time Machine snapshots. Even if you don't have an external drive for Time Machine, the system will store snapshots of changed files.

A program such as Carbon Copy Cloner (which is useful for creating custom back-ups of data) can see these snapshots, show their size, and delete them. They cannot be deleted in the way a file can, as they are part of the structure of the file system.

By virtue of the users concerns related to /System/Volumes/Data

They are interested / concerned in Reducing System/Volume/Data which is a common question. 

1 -  System data taking too much in MacOS Sono… - Apple Community

2 - Time Machine Local Snapshot won't delete - Apple Community

3 - Over 60% storage blocked by System Data - Apple Community

How to free up ‘System Data’ and other storage on your Mac from a fellow colleague @ neuroanatomist

Use another application to see where space is being used  Storeograph  on the Apple Apps Store 

View APFS snapshots in Disk Utility on Mac

Suggest getting an External SSD Drive and start moving your Pictures, Videos, Music, iPhone Backups, Other Developer related data and any other large files you have control over, OFF the Internal drive and Onto the External

There are  two effective ways to remedy this issue:

1. Quick Fix Actions:

 For Apple Silicon computers, use Disk Utility to erase a Mac.

For Apple Intel computers, use Disk Utility to erase an Intel-based Mac, then reinstall macOS.

Always make a Time Machine backup before proceeding.

Migrate only the user account, not the entire system.

   Reinstall only the necessary applications from the Apple App Store or directly from the developers.

2 - Generally

When the user discovers this issue, it’s likely because the computer’s internal drive capacity is small, such as 256 GB or 512 GB.

Unfortunately, the user’s storage needs may have increased since the computer was purchased.

To future-proof the computer, consider spending extra money upfront on a larger drive capacity and adding more unified RAM.

Note - On Apple Silicon and newer computers. The SSD Drive and the Unified RAM are Soldered to the Logicboard and can not be upgraded.

System Data is how Spotlight labels stuff that doesn’t fit in other categories. It’s your data, mainly in the ~/Library folder. Examples include MS Outlook attachments, cloud storage caches, etc. There is no magic bullet, you either need to dig in and find the files.

How to free up ‘System Data’ and other st… - Apple Community

To really see the Used versus Free space

What has been presented in your image is " Eye Candy " which is rather useless

Disk Utilities is the place to go

From another contributor @etresoft regarding Free Space and Available Space 

Free vs available disk space huge differe… - Apple Community

Quote >>  “ The "available" storage is the amount of used storage that the operating system could automatically delete if it felt that it was really necessary.

The "free" storage is the amount that you can actually use for something.

There are system processes that run in the background and automatically delete some of the "available" storage and convert it to "free". If you completely run out of storage, then those system processes will try a little harder. When you "delete" files you are just hinting to the operating system that you don't need those files anymore. The operating system will eventually remove them, but on its own schedule.

Certain tools will allow you to force the issue and manually clean up some of this storage and manually delete local snapshots. But that is only temporary. "  << End Quote 

Purgeable Space is controlled by the Operating System and not the user 

Get detailed information about a disk in Disk Utility on Mac

achenphys wrote:

Thanks very much for your explanation. I understand the logic of how it works. I just somehow cannot accept that 100+ GB of space is used by the "system." To me, it is a weird design. I was wondering if there is anything else that take the space.

It looks like it is just a similar issue as iOS

Accept or Not accept

The end result will remain unchanged

There has been sufficient advice offered, from two separate and independent Contributors with a combined experience of about 41 year using macOS

The User ( you ) can make an informed and educated choice what remedial actions are  required for this computer.

The suggestions have been put forth on a volunteer basis, in good faith and in the best interests of the computer which do not always align with the users’ expectations 

achenphys wrote:

Thanks very much for your explanation. I understand the logic of how it works. I just somehow cannot accept that 100+ GB of space is used by the "system." To me, it is a weird design. I was wondering if there is anything else that take the space.

As stated, System Data is just a category. If it helps to understand, it used to be called "Other". They are files that macOS does not categorize as Documents, Photos, Music, Applications, etc., but they are still your data. "System Data" is not part of macOS, that is a separate category.

Options and tools have been suggested for determining what comprises 'system data' on your system. You can choose to follow those suggestions, or not.

One other note: your macOS is listed as 55.82 GB and that is larger than I'd expect (should be 20-25 GB including Apple Intelligence). You likely need to reinstall macOS.

How to reinstall macOS - Apple Support

I'd forgotten about it until just now, but Daisy Disk has a free trial which, I just checked, shows system data as well.