“Other” Storage Over 300GB On A New iMac

How may upGrades has this computer experienced in its' lifetime ?

The machine maybe experiencing the cumulative effects of several upGrades and acquired the " Residue Effects " of all the upGrades

It is generally a good computer practice to alway keep at least 20% to 25% of the Total Drive Capacity’s as Empty Space. Allowing the computer to drop below these guidelines may eventually, cause unintended consequences.

There is Purgeable Space and there is Empty Space.

Purgeable Space which is Controlled by the Operating System. When the Operating Systems decides the computer needs additional Empty Space, it will move a portion of the Purgeable to Empty space

AFAIK - there is no User Actions to hasten this transition from Purgeable to Empty Space

It can day or longer before this will occur.

The links below will assist in identifying what is taking up space on the Internal Drive and provide possible ways to remove data that is under the direct control of the User ( Home Folder ) . 

Rebuild the Spotlight index on your Mac

Free up storage space on your Mac

GrandPerspective 

How to delete Time Machine snapshots on your Mac.  

Often caused if the Time Machine Drive has not been attached  to the computer and TM Backup is set to run on a Schedule. 

TM Backup will make Snap Shot on the Internal Drive awaiting the TM Backup Drive to be attached. 

Only then will the Snaps Shots be transferred to the External Drive and deleted the Internal Drive.

Is the User using some Cloning Software ?

https://bombich.com/kb/ccc6/automated-maintenance-ccc-safetynet-folder

See used and available storage space on your Mac

Locate backups of your iPhone, iPad, and iPod touch

It see 19.1 GB of IOS Files in one of your pictures

IIs there a Suite of Adobe Application  used on this computer ?

They may create some very large cache files that can be removed. Though, the Adobe cache files will be recreated as the Applications needs them.

https://helpx.adobe.com/ca/premiere-pro/kb/clear-cache.html

The final word from Apple on Managing the " Other/ System Data “ Category

Other / System Data: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.

See, What is “Other” storage on a Mac, and how… - Apple Community

also, when was your last restart?

when was your last Time Machine backup?

How much streaming content do you consume?

do you use Adobe software or other software that may create file versions or retain history? Or, connect to a cloud?

other storage is system managed and should free as space is needed on your device.

ww1903 wrote:

Thanks for all of that info. There have been zero upgrades. It was purchased in 2021. Earlier this year I set it up and migrated certain things. I use Ae and Ps but keep all assets on an external. Because I couldn’t find what exactly it was, even with 3rd party scans and “cleaners”,

Ouch and not really a good idea then or since the update or upgrade

Any Third Party Applications that will interfere with the normal operation of the OS,  is an invitation for disaster. 

Certain Applications maybe available on the Apple Apps Store - this only means the Developer is prepared to pay Apple a portion on each sale. 

What the Application may do to the computer is up to the User to check this out before purchase

Any of the below should be removed as per Developers Instructions 

1 - Disk Cleaner 

This will include CleanMyMac , aka “ BrickMyMac “

MacKeeper,

Dr Cleaner Pro Plus

Open Cleaner one Pro

Macmechanic

Clean my Mac x.

Read some of the posting and arrive at your own conclusions.

I went ahead and restored it to factory settings and started over, and it is gone now. Really didn’t want to do that because I liked Big Sur, but Apple wins. I was forced to update.

There are ways to avoid the upGrade

System Preferences or in Ventura System Setting and refer to below image

Uncheck certain elements in that image and presto, no more upGrades.

It may still Alert you of a possible Qualifying upGrade but that will be it.

Thanks again for your informative response. Unfortunately, these things seems to only happen to people who are happy with their os, and don’t want to update every time there is one. It’s helpful to know that it’s not permanent and will adjust if or when it happens again.