Reducing system data usage on my new MacBook Air

Disregard the confusing Storage eye-candy, it has been inaccurate for more than a few macOS versions.

If you want an accurate read on Storage Space, use Get Info on the Macintosh HD or open Disk Utility and select the Macintosh HD.

If you did a search here, you will find literally hundreds of posts on this exact topic that includes what "system data" is, and isn't. You would also find potential options on how to deal with it.

In a nutshell, "system data" is managed by macOS. There is little value trying to micro-manage it yourself.

If you're curious, it contains things like:

• APFS local snapshots (both Time Machine and system-created)
• System caches and logs
• Virtual Memory files
• Application support files that aren’t user-specific
• Extensions, fonts, and other system-level resources
• Spotlight indexing
• iCloud Storage of infrequently-used files
• Leftover app junk, installer packages, or temporary items that haven’t been cleaned up yet

An often asked question with No One Size Fits All solution

Page 1 of 2 specific to your query

Search - Apple Community

+ 1 and amen to that

🦉-53

Your question re System Data has been outlined in some detail

Solutions have been provided

what actions the user chooses to do with this info is up to you

Just to add

The more  popular and effective ways 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