Not enough disk space (occupied by Icloud)

As I mentioned before, https://discussions.apple.com/thread/7852353 explains how to delete files in the /cores folder. It looks like you are running Big Sur, and that link relates to an earlier version of the operating system, but I think it still is valid.

In your Etrecheck output, there are two pieces of software you have, Kapersky anti-virus, and Clean My Mac -- you should consider uninstalling them completely to see if it help prevent the crashes that have been causing files to be written in /cores. Normally Macs don't need or use programs like anti-virus and Clean My Mac. Some users have reported problem in the Apple Discussions that have been traced to those types of programs.

For more about what /cores are used for and how you can delete those files, see this: https://discussions.apple.com/thread/7852353

Not sure why you have so many core dumps. If you delete those files, they will start getting created again unless you figure out why your computer is crashing so often.

OmniDiskSweeper is free and allows you to sweep through your entire drive and sort everything that is found by file size. This may help you identify large things that you no longer need, or if you do need them, you could move them to external storage.

Do you have an iPhone? If so, look in your user Library folder under the Application Support folder for a Mobilesync folder. Inside that folder are iPhone backups. Keep the ones you need, but old ones that are no longer useful to keep can be deleted.

Another folder you may have is in the user Library/iTunes and it is called iPhone Software Updates, files in that folder, if left over from old iPhone software updates, can be deleted to save space.

Restart your Mac, empty the trash, and also review what is in your Downloads folder in case those are no longer needed.

Old installers can be located by downloading Find Any File and searching for files whose names include

.dmg

those are installer files that you may no longer need.

The Other category is a potpourri 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

They 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.

The System files are exactly that. They should not be deleted, modifies or altered in any way. Doing so will cripple the computer completely.

Purchase an External Drive - not too expensive - and move as much of your personal files to the drive.

As was already said, don't touch System.

Also,

cores

... this is a folder at the root level of your drive that you should not be able to access. Yet you can see it in your screenshot and can even see files inside it? I cannot do that on any of my Macs, the permissions are set to prevent any user from modifying or even accessing that folder. Don't touch any of those "cores" files, and the fact that you can see into that folder makes me wonder if you have altered your system in some unusual way.

Do you have some sort of custom installation, have you modified the system or permissions in some way? That might be part of the space problem you are experiencing ... it also looks like you have the smallest possible disk for a modern Mac, 128 GB. As was also suggested before, it would help to obtain an external drive and move some of your PERSONAL (not System) user files to that to save space on the internal drive.

More on this -- "cores" contains core dumps from times that your computer crashed. On all my computers "cores" has zero space used, there are no files in that area. So the fact that yours is using more than half of your disk is a problem.

Do you have any idea why yours has so many core dumps inside "cores"? One way to unravel this might be to download and run Etrecheck, a free diagnostic program written by one of the experts in these Discussion forums. Then post the output here, people may be able to find out from Etrecheck's output why your computer is crashing so often.