Finder not showing the accurate space being used

Storage space with the APFS file system is very complex and is not easy to understand especially dealing with smaller file sizes (yes 12GB is not significantly all that large in this context).

The only important value when looking at how much useable storage you have available at any particular moment in time is by using Disk Utility as @Ronasara mentioned in order to check the Free value listed there. The value shown in the Finder is "Available" storage which unfortunately is a terrible term to use here because it is not storage that is immediately usable....instead "Available" means that space will become usable at some unknown time in the future. The "Available" value is also shown in Disk Utility where it is shown to consist of "Purgeable" space with the remaining space being "Free". I personally think the Finder should be showing the actual Free value instead and within Disk Utility it should show as "Purgeable" instead of "Available" as these terms make much more sense to most people. "Available" is not the same as "Free".

The next thing to consider is how the APFS actually works. When you copy a file within the same APFS volume....you do not actually create a brand new second copy of the data like happens with most other older file systems. Instead on an APFS volume, only a small link file is created to point to the original file. This means when you delete either one of the two "files", you are only deleting a small link file....the actual data still remains on the APFS volume until the second "copy" or link is deleted. This is why you don't see a decrease in the Free space when copying files on an APFS volume.

Another thing unique to the APFS file system over other older Apple file systems is that APFS file systems can include APFS snapshots which are usually utilized by backup software such as Time Machine & other third party options. If an APFS snapshot exists, then you delete a large amount of data....that data may still reside in the hidden snapshot until that snapshot is deleted which should happen automatically at some point...maybe a day, or a week depending on the app used to create that snapshot. Backup snapshots will not delete automatically until they have been transferred to external media...even then it may take days for it to happen. Plus some third party apps may have a policy to retain certain snapshots for longer for some reason.

Plus remember when dealing with small amounts of data (even 12GB) that macOS and your apps may be writing and/or deleting items at the same time so it is hard to say what the changes in the "Available" & "Free" values may indicate without looking more closely at every change on the system.

Yes that is how it works. Definitely not easy to explain as you can see.

FYI, I have seen a couple forum contributors post regarding a setting to toggle in CCC to control some aspect of CCC's snapshotting....I believe it may have something to do with keeping some CCC snapshots around longer. You may want to investigate this aspect of CCC snapshots.

Plus when any changes occur to an APFS file system, macOS will first write the changes to the disk followed by updating any behind the scenes links to properly integrate the changes to the previous state of the file system. Because the APFS file system must first write to the drive its pending changes (new data, edits, deletions), there must be enough Free storage space available to write these changes even when deleting data. This makes the APFS file system much less likely to become corrupted due to an interruption such as a power outage.

Remember this behavior is only for the new APFS file systems utilized by macOS 10.13+.

Something else regarding APFS file systems you may want to be aware of....if you look closely at the drive layout of macOS 10.15+ system, you will notice that multiple APFS volumes are included within a single APFS container. Each APFS file system within a single hidden Container shares the same storage pool. You can see this within Disk Utility by how the "Free" space is the same for each of those APFS volumes. Each APFS volume within a single Container is its own entity that requires it to be mounted individually.

Containers are basically like a traditional partition found on older versions of macOS, Windows & Linux systems. The only difference between an APFS Container and a traditional partition is APFS Containers may have multiple volumes within them. A "Volume" is a mountable file system entity.

Not many websites have a short clear explanation of these new APFS features & behaviors which I feel comfortable posting here.

Here are a few links which I did not have time to look for or post previously (still can not find the link for the one site which had an explanation of the copy feature that I feel safe posting...the best one I could find today has advertising for products which are detrimental to the health of macOS even though they are legitimate products so I'm not posting it):

https://en.wikipedia.org/wiki/Apple_File_System

About the read-only system volume in macOS Catalina or later - Apple Support

Signed system volume security in iOS, iPadOS, and macOS - Apple Support

If you want to accurately know how much free space is on your HD, the best way is to open Disk Utilities and see it there.

You're welcome. I hoped you would appreciate the extra information...your previous post seemed to indicate interest in understanding the new changes.