My system data takes up to 140GB, can I know how to clear them?

Hi there dymls,

We understand you're trying to free up storage space on your Mac, and we'd like to share a resource that can help.

Take a look at it here: Free up storage space on your Mac

Specifically, the section below may help:

"Free up storage space in other ways

• Manually delete unneeded files by moving them to the Trash, then emptying the Trash. Deleting unneeded music, movies, and other media can free up a lot of space, as can deleting files in the Downloads folder.
• Delete unneeded email in the Mail app. To delete junk email, open Mail and choose Mailbox > Erase Junk Mail. To delete email you've moved to the Trash mailbox, choose Mailbox > Erase Deleted Items.
• Connect an external storage device to your Mac, then move files to that device.
• Compress files so that they use less storage space.
• Make sure that your Mac is using macOS Sierra or later, which includes space-saving features like detecting duplicate downloads in Safari; reminding you to delete used app installers; removing old and unused fonts, languages, and dictionaries; and clearing caches, logs, and other unnecessary data when storage space is needed."

The information here may also help: See used and available storage space on your Mac

Cheers!