imac 2012 random restart

This panic log is associated with the disk system. A problem with the Disk Queue Manager. I'm not sure of the solution, if any. Some questions: a. Have you removed the internal drive? b. What settings are enabled in Energy Saver preferences? c. Does the problem also happen when in Sleep mode?

The error was first noted in Mojave. So far, I cannot find a definitive solution, if there is one. I am guessing it's a hardware issue. Thus, it could be caused by the failed or corrupt internal drive. Can you fix the drive or has it failed? I could also be caused by your external SSD's enclosure, cable, or port used on the computer.

Dealing with Kernel Panics

Disconnect any third-party peripherals including any USB hubs. How to use safe mode on your Mac, Use safe mode to isolate issues with your Mac - Apple Support then boot the computer into Safe Mode: Use safe mode to isolate issues with your Mac - Apple Support and Playing Safe- what does Safe mode do? See Diagnosing problems- crash, freeze, panic, or spinning beach ball?, Don’t Panic! Understanding & Troubleshooting Kernel Panics in macOS, How to fix kernel panics after installing OS X updates | MacIssues, and If your Mac restarted because of a problem - Apple Support.

Kernel panics are indicative of possible hardware failure, so you should Check your Mac with hardware diagnostics or AHT. Kernel panic logs are found in: /Library/Logs/DiagnosticReports/ folder.

If you have no success figuring what is happening then you may need to examine the software you have running when the panics occur. Be sure it’s all current. If you must to resolve the problem erase the disk and reinstall macOS. Follow this outline to reset the computer to the factory-new state: Factory reset of your Mac - Apple Support.

Boot Into Safe Mode

1. If your Mac isn’t already shut down, then shut it down and wait at least 30 seconds before rebooting.
2. Immediately, at or before the chime, press and hold down the SHIFT key. 
3. Release the key after the Apple logo and progress bar appear.
4. Safe mode startup is much slower than normal startup, so be patient.
5. When the Login Screen appears enter your admin password. If you use automatic login, then this means you are in safe mode.

Do you have such problems with any other programs or only with Chrome? If it is only with Chrome, then I suggest you stop using it and stick with Safari. Otherwise, I can only suggest downgrading to Mojave: How to Downgrade from macOS Catalina to Mojave or Earlier.

The problem might occur if you upgraded over an existing system that was malfunctioning. Since it would be too late to fix the old system, all you can do is try to fix the new one or erase the drive and install Catalina from scratch.

Panics can be hard to track down. IMO, it's usually faster to start from scratch, like so.

Install El Capitan or Later from Scratch

If possible, back up your files.

1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
2. Select Disk Utility from the Utility Menu and click on the Continue button.
3. When Disk Utility loads select the target drive (out-dented entry w/type and size info) from the Device list.
4. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
5. Set the partition scheme to GUID.
6. Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
7. Click on the Apply button, then wait for the Done button to activate and click on it.
8. Quit Disk Utility and return to the Utility Menu.
9. Select Install OS X and click on the Continue button.