How can I clear System Data on my MacBook Pro?

"System Data" is a bucket for things that the system doesn't recognize as belonging to the other named types of data (Applications, Mail, Music, etc.)

I suggest using DaisyDisk or similar app to investigate what is taking up space on your drive. It's available directly from the vendor as well as from the App Store.

BTW, do you have any iOS devices that you back up to your Mac? Those backups are hidden and typically take up a lot of space.

do you have more than one account on that Mac?

see this post—

"Then I looked and there was a second "Admin" User. So I deleted that.

Now everything looks like we're normal."

ref: HELP! Storage taken up by mysterious "oth… - Apple Community

The only way I could drop that number quite a bit was to erase the drive, reinstall the OS and migrate all back. Had to do this on three Macs with success.

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

Some of which as been already mentioned

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

The category is a collection of files which include:

• System temporary files

• macOS system folders

• Archives and disk images (.zip, .iso, etc. - often found in the Downloads folder)

• Personal user data

• Files from the user’s library (Application Support, iCloud files, screensavers, etc.)

• Cache files

• Fonts, plugins, extensions

• Other files that are not recognized by a Spotlight search

• Media files that cannot be classified by Spotlight as a media file because they are located inside of a package like Developer Files which Presently Occupy 2.63 GB as per your image

Though, as hat appears to be some type of a Developer working on this machine

Using a 500 GB Internal Drive is going to be a challenge at best

• If using a Cloud Based Services to sync files,  like iCloud and One Drive. These can also occupy space on the Internal Drive 

The files can be located anywhere on your hard drive. The files that you have control over are located in the Documents, Downloads, Pictures, Music and Movies folders. 

You can use either of these two free apps, GrandPerspective , to find the largest files on your drive so you can determine if they can be deleted or moved to an external HD for storage.  

Another Application to find and analyze what is using space on the drive is Etrecheck >> Clean up

To close out my portion in this question

Unfortunately or fortunately depending upon ones' perspective

The suggestion from @tbirdvet is only a " Quick Fix "

It will not cause the Internal Drive to grow any larger that the current 500 GB Drive Capacity

The implications being, that on the next purchase

Spend the extra money, up front, for a computer that has a large enough SSD Drive and RAM for the current needs and add in what you project your needs will be for the next 3 - 5 Years ( as best as you can )

Doing so will, generally Future-Proof the computer