MacBook Pro System Data using excessive storage

402 GB is large enough that I’d investigate it, but System Data isn’t just macOS. Apple says it can include caches, logs, virtual-memory files, app support files, plug-ins, and other data that doesn’t fit another storage category.

Since you use Adobe software, I’d check that first. If you have Premiere Pro or After Effects, both can build sizable media/disk caches. I’d manage those from the Adobe app’s own cache settings rather than manually deleting files from your Library.

Also check System Settings > General > Storage > Documents > File Browser and look for unusually large folders. Don’t delete anything you don’t recognize, and make sure you have a current backup before removing large amounts of data.

Apple explains what System Data includes here: Change Storage settings on Mac

If you tell us which Adobe apps you use and whether Time Machine is enabled, that would help narrow down where the 402 GB may be coming from.

Please view this guidance from Apple on the subject of freeing up space:

Free up storage space on Mac - Apple Support

Find and delete files on your Mac - Apple Support

And this user tip: How to Use Finder to Clear “System Data" on a Mac (Thank you, @TheLittles!)

Also, if you have enabled Time Machine to back up your Mac automatically but do not keep your backup drive connected all the time, then MacOS keeps a number of Time Machine snapshots on the drive as part of the backup process.  These TM snapshots can occupy a significant amount of drive space. You can disable the creation of these many TM snapshots by setting TM to backup manually rather than automatically at intervals.

You can view and manage these Time Machine snapshots in Disk Utility. View APFS Snapshots in Disk Utility on Mac - Apple Support 

You can also use apps such as Storeograph from Etresoft, Inc  or OmniDiskSweeper from Omni Labs  to find the large files on your drive.  Once you've located these larger user files, you can relocate them to another drive and/or delete them if they aren't needed. Especially consider relocating your Music and Photos libraries to an external drive and accessing them from there.

Move your Photos library to save space on your Mac - Apple Support

how to move music library to external har… - Apple Community

Droll_Pineapple wrote:

I am concerned about the level of system data being generated and wonder why the OS does not clean it up.

That's because it has absolutely nothing to do with the operating system. This is an extremely common problem. Unfortunately, Apple's built-in Storage software only serves to confuse people and make the problem worse.

Does anyone know which programs may be doing this?

There's no way to tell.

You will need to download a 3rd party storage management app to tell you which folders are using an unusually large amount of storage. I can't recommend one because I develop one. The forum rules forbid me from posting a link to my app. I'm obviously not going to recommend other apps. If I thought they were great apps, I wouldn't have written my own.

Droll_Pineapple wrote:

I have previously downloaded third-party software to try and identify unnecessary data caches and files, including one with the same name as your handle.

I don't know of any app with the "Etresoft" in the name. My apps have distinctive names, and do often include "etre" as a way to avoid trademark complications. But "Etresoft" is the company name, not an app name.

There's no such thing as "unnecessary data caches". That sounds like scamware.

I did not find the UX helpful, as it did not clarify which files could be deleted safely, and I do not see any duplication in the system.

There's really no way to tell which files can be deleted safely. Years ago, this problem was commonly caused by Time Machine local snapshots. While that's still technically possible, in the past few years, I don't think I've seen the same cause more than once. It could literally be anything.

If you are talking about my app "Storeograph", then the "Explorer" package is an in-app purchase. Older versions of my EtreCheckPro app also have a more primitive Storage tool for free. If you have specific questions about specific files, you can use the apps' built-in support options. And if you don't want to do that, or if you're using some other app, you can always ask right here.

But the problem should be very obvious. 400 GB is a lot. It should stand out easily. Don't waste time looking for small files. If it isn't 10 GB+, ignore it.

I'm not sure what you mean about "duplication". Don't waste any time looking for duplicate files. They don't really exist. You can create them, buy you really have to try hard. I did add a duplicate file finder to Storeograph because I know people think that's a problem. I only consider it a problem in terms of potential confusion about which duplicate is the "real" or current version.