Size for Users displayed totally different than actual size

A lot of the data can be found in the hidden Library folder within your home folder. Apple likes to keep this Library folder hidden by default, but you can easily access it by selecting the "Go" menu in the Finder and holding down the Option key which will reveal the hidden Library folder option. Except for sometimes needing to delete small corrupted .plist preference files from the Preferences folder, a user should not really delete or modify anything in this hidden Library folder.

As for the size of the item labeled "Documents" I think you may be misinterpreting how this works. I believe it means all documents within your home user folder even if they are on the Desktop, or within the Downloads folder. I don't look at the macOS storage management area since I know it will many times show incorrect values. The only important storage value for me is the actual "Free" space value.

Please review my other post where I explain the macOS storage terminology. Unfortunately "Available" does not mean what you think it does....it is very unfortunate that Apple decided to use that term and promote it everywhere in macOS. You need to be concerned about the amount of actual Free space that can be utilized.

Storage help -- understanding macOS storage terminology & space usage -- hwtech - Apple Community

MAUIOxo wrote:

I've checked both the ~/Library/... and the /Library folder but I can't find out where the space is not released.

Avoid the main system "/Library"....you should not touch anything there since that is for the main macOS system. You can only control the storage located in the hidden Library folder within your own home user folder "~/Library".....even that one you need to be careful as well.

The really strange thing for me is after even deleting XCode which is 23 GB the newly available space can not be seen as free. Well, after a couple of restarts and waiting it did show up in Apple Logo > About this Mac > Harddisk section as free finally. But, there is also plenty of GB of System Data and it seemed like not all of the 23 GB were released.

Storage on an APFS volume is complicated due to how the APFS file system works. Plus all the new privacy & security settings add even more complications since it can even prevent you from even accessing some locations, essentially hiding files. Usually if you delete something and the Free space does not increase, then it may mean the deleted items are still on the drive in a hidden APFS snapshot which are usually associated with backup software. In the "Storage Help" link I provided in my previous post, there is a link within it which has a link to an Apple article for viewing & deleting APFS snapshot (if they exist).

You mentioned you have other macOS user accounts on this computer. Have you checked those other macOS user accounts? They may contain more data than you realize.

And it also happened in the past that I deleted XCode and wanted a fresh installation which wasn't possible anymore as the space was not released and in total there was not enough space available to Download and Install XCode even it was installed couple of minutes before.

I haven't installed XCode in a while, but if it uses an installer app which extracts & expands files contained in the app, then you have the expanded extracted files + the XCode installer app you downloaded as well. When you are running on the edge of not enough Free space, this is the type of things that can happen.

Therefore, I thought - well, maybe I reinstall the OS (Monterey) again to get these files back. As I am not the only user on this Mac, I wanted to reinstall it without loosing data of other users and also maybe not lose installed Apps.

Do you have a backup of this system? If not, then you should make sure to make a backup of it now so you at least have all the user data within all the macOS user accounts on this Mac. Apple includes the Time Machine app to easily backup your Mac.

I don't know what to do now. What I really want to do is have a clean installation without deleted system files and deleted files that were needed by XCode to start correctly and do not crash. This installation should be without deleting programs if possible and without deleting files of other users. If this was done, I wanted to reinstall XCode. And I assume this should be possible then even without having too little disk space. Why do I believe this? Because it previously was like that and I could install and use it.

How can I achieve this with the above story in mind?

Unless you can delete or move some data to external media, you probably won't be able to fix anything or reinstall XCode since you have so little Free storage space. While I did install XCode years ago, I don't recall the details and I've never uninstalled it (or deleted it) & tried to reinstall it, so I won't be of any help in that respect.

Here is an Apple article for freeing up space on the boot drive:

Free up storage space - Apple Support

If you cannot acquire more Free storage space, then your best option would be to perform a clean install of macOS which involves first erasing the disk, followed by reinstalling macOS and restoring the macOS user accounts from a backup (avoid restoring your apps since you are now having problems reinstalling XCode) unless you have a good backup made prior to these issues & the deleting of XCode.

Edit: Accidentally clicked "Post" button instead of the bold icon....still had some corrections to make.