System data says 167.4. GB [Shift] [control] [.] reveals 99 GB; What about the other 68 GB?

Showing hidden files is fine but that does not explain how Apple has sorted files into "System Data" versus the other categories. That sorting can vary depending on a number of factors so it doesn't make clear what is in "System Data." I would ignore "System Data" and instead figure out where you disk space has all gone.

From your screen shots, I see the following in your user account:

Desktop: 81 GB

Downloads: 76 GB

Documents: 16 GB

Library: 100 GB

Pictures: 36 GB

iCloud Drive Archive: 46 GB

Other various folders (Developer 2 GB, Music 8 GB, podcasts/TV 0.5 GB, other users 1 GB)in your user account: 12 GB

That totals crudely counted up ~ 370 GB for your user account.

But there is more, MacOS (35 GB), Applications folder for all users (not just your user Application folder) (35 to 50 GB), Library (system, not your user library) 10 GB ... plus other system files that are outside of your user area so they aren't showing in your listing ... add these in and it can come to ~ 100 GB more.

For grand total of > 475 GB, which agrees roughly with your screen which says 491GB out of 494 GB used.

So you have basically run out of space.

The utility DaisyDisk will give you a much more precise rendition of where your space is being used.

A Mac won't operate properly with 15%-20% free space, you have < 1% free space. So you are on the edge of a lot of trouble.

For one thing, review your Desktop and Downloads folders, those take 150 GB right there. I am sure much can be safely deleted. You can also move your 36 GB Pictures folder to an external drive, or simply use iCloud to store the full size originals with much smaller snapshots physically taking space on your Mac. Apple has detailed instructions for both those options. You can also save 7GB by using Messages in iCloud.

Your user Library has 100 GB. DaisyDisk would tell you why that is, but Mail and Messages are using 15 GB alone. I'm sure some of that 100 GB could be reduced.

In my earlier post I provided links that may help:

Free up storage space on Mac - Apple Support "The category named System Data (or Other) is a general category that measures the storage space used by all Apple and third-party files that don’t belong to any more specific category."

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

freeing up storage space & system data - Apple Community

Not sure what you are searching for or what that key combination is doing for you, but what Apple calls "System Data" is actually a melange of MacOS files and various user files. It varies from Mac to Mac in a way that is not consistent.

Also it is unclear what "practices" you have put in place to suppress System Data, or whether they are helping more than hurting.

The latest version of Sequoia is 15.7.2 and your profile shows a much older version. Updating to the latest version fixes bugs and improves security.

From Apple:

Free up storage space on Mac - Apple Support "The category named System Data (or Other) is a general category that measures the storage space used by all Apple and third-party files that don’t belong to any more specific category."

For instance, even though there is a category in the MacOS "storage" audit called "Photos," on my Mac System Data includes MANY large Photos Libraries.

Apple's "accounting" for usage of disk space through the "Storage" button leaves something to be desired. On one of my Macs it says calculating and never reaches a final result.

One of my Macs shows 90 GB for System Data; my wife's Mac shows about 25 GB for System Data. Because Apple says it can include "third party files," it can really include almost anything. In some cases, people have reported that System Data even includes some attachments from email files. So 100 GB or 200 GB or more is not out of the question.

I suggest that you obtain a good commercial tool such as DaisyDisk that will (when you run it as administrator) tell you where EVERYTHING is on your computer and how much space it is taking up.

See also this informative article: How to free up ‘System Data’ and other st… - Apple Community

In addition, Owl-53 has instructions for how to clear everything out but this requires erasing your drive:

freeing up storage space & system data - Apple Community

steve626 wrote:

Not sure what you are searching for or what that key combination is doing for you, but what Apple calls "System Data" is actually a melange of MacOS files and various user files. It varies from Mac to Mac in a way that is not consistent.

Also it is unclear what "practices" you have put in place to suppress System Data, or whether they are helping more than hurting.

The latest version of Sequoia is 15.7.2 and your profile shows a much older version. Updating to the latest version fixes bugs and improves security.

From Apple:

Free up storage space on Mac - Apple Support "The category named System Data (or Other) is a general category that measures the storage space used by all Apple and third-party files that don’t belong to any more specific category."

For instance, even though there is a category in the MacOS "storage" audit called "Photos," on my Mac System Data includes MANY large Photos Libraries.

Apple's "accounting" for usage of disk space through the "Storage" button leaves something to be desired. On one of my Macs it says calculating and never reaches a final result.

One of my Macs shows 90 GB for System Data; my wife's Mac shows about 25 GB for System Data. Because Apple says it can include "third party files," it can really include almost anything. In some cases, people have reported that System Data even includes some attachments from email files. So 100 GB or 200 GB or more is not out of the question.

I suggest that you obtain a good commercial tool such as DaisyDisk that will (when you run it as administrator) tell you where EVERYTHING is on your computer and how much space it is taking up.

See also this informative article: How to free up ‘System Data’ and other st… - Apple Community

In addition, Owl-53 has instructions for how to clear everything out but this requires erasing your drive:

freeing up storage space & system data - Apple Community

Merci and thank you for a credit my friend

And excellent work there tooooooo

🦉-53

Two cents if you please

The Only reliable too built into macOS that Weill give a far more accurate view of Used Space versus Free Space would be Disk Utilities

All other reporting methods are only Eye Candy

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 

@steve626

In the sole interest of Continuity

This other posting by OP may come into play on this question ?

How to safely remove Linux UTM and clear … - Apple Community

steve626 wrote:

Owl-53 wrote:

Merci and thank you for a credit my friend

🦉-53

De rien!

I remain a student in Professor Owl-53's Master Class!

Too kind

As I have been fortune to be a Student of another Contributor ( BDAqua ) for many years and still am

It is good to indirectly pass along to same to others

Re OP issue

Notice Adobe Creative Cloud plus iCloud ( Archive ) in OP screen shot

Good sources for System Data related issues

Owl-53 wrote:

Merci and thank you for a credit my friend

🦉-53

De rien!

I remain a student in Professor Owl-53's Master Class!