OS 12 Why Does this crash happen?

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

If after the normal reboot the problem persists please download and run Etrecheck.  The free version is sufficient.

Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and after clicking on the Reply button use the Additional Text button to paste the report in your reply.

Check Etrecheck's Privacy settings and make sure the checkbox for full disk access before running:

Then we can examine the report and see if we can determine the cause of the problem.

Unless you're using a true VPN tunnel, such as between you and your employer's, school's or bank's servers, they provide false security from a privacy standpoint.  Read these articles:  Pubic VPN's are anything but public and Security Risks: The Dangers of Using Free VPNs (eccu.edu).  

Also I saw a line about BitCoin Expert. What's that about?

The error message in the screenshot tells you what to do although it may not be completely obvious because Disk Utility hides the APFS Container from view by default.

Within Disk Utility click "View" and select "Show All Devices" so that the hidden Container appears on the left pane of Disk Utility. Run First Aid on that hidden Container. It will also automatically run First Aid on all of the APFS volumes within that hidden Container. It looks like maybe the Terminal command you used may have done that, however, did that scan of the Container resolve the previous error or is that error still there.

If after several First Aid scans of the hidden Container the error remains (while booted into Recovery Mode), then the error cannot be fixed. In that case erasing the disk followed by reinstalling macOS & restoring from backup will be needed.

The question then becomes what caused those errors. Is the internal Hard Drive starting to fail or did something else cause it? You can check the health of the internal drive(s) by running DriveDx (free trial period) and posting the complete text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar.

The public in Public VPNs isn't referring to a place but the VPN itself. They don't insure security. I wouldn't use them unless they are provided by an employer, school or financial institution.

As for BitCoin, do you invest in bitcoin? If so I hope you have disposable income to do so.

illstudio wrote:

I'm guessing the news isn't good. Can the Late 2015 3.2Gz iMac have it's HDD replaced? Im assuming the 1 Tb is failing drive. I have the org fusion drive setup. Any HDD replacement suggestions, if replacement is possible? THX.

<DriveDX log.log>

The DriveDx does show that the internal Hard Drive is failing with currently 64 Reallocated Sectors. Currently there are no Pending Sectors so all of the identified bad sectors have been reallocated at the time of the report was run.

While the internal Hard Drive can be replaced, this is not a simple matter. It is much easier to just use an external USB3 or Thunderbolt2 SSD instead for your macOS installation. A USB3 SSD will give about the same performance as your Fusion Drive, while a Thunderbolt2 SSD may give you even more performance depending on the SSD. Plus when you retire this iMac, you can re-purpose the external SSD to other things with another computer.

illstudio wrote:

Hi, I have PureVPN which I rarely use cause it causes some website response problems. My iMac is never in a public place, doesnt leave my home office.

BitCoin Expert is an app that appears if I launch it, above desktop image where "time/date" shows (Forget what that area is called)? Not married to it, so it can go. Thanks

If BitCoin Expert launches when you launch PureVPN, then you just discovered that most VPNs targeting consumers are pure junk and are not focused on privacy or security. I would be very concerned what that extra app is doing to your system besides impacting system performance since I'm sure at the very least your system is being used to mine BitCoins.

Consumer VPNs do not provide the privacy & security that you believe. VPNs are only useful when accessing network resources on a business network. People should read the following article for more details:

https://gist.github.com/joepie91/5a9909939e6ce7d09e29