2017 iMac just started to randomly freeze and reboot with kernal panics. Help! EtreCheckPro report attached.

1) When did you upgrade the RAM from 8 GB to 40 GB...?

If some time ago, recheck to make sure that all modules are firmly seated in the slots.

If recently, where did you purchase the 16GB modules that you use to upgrade the RAM?

2) Those 3T Fusion Drive setups can become iffy over time and you have no Time Machine or other backup.

Before you do anything else, I highly recommend that you make a Time Machine, CarbonCopyCloner or SuperDuper backup on at least a 4T external hard drive.

As a test, turn off Sleep and see if the issue still exists. On other sites, there are reports that sleep can an be an issue.

Are you using a second monitor?

These were on this site: https://softwaretested.com/mac/how-to-fix-crashes-from-userspace-watchdog-timeout/

You can save the Mac, however I'd start saving $ for a new one as yours is getting close to being obsolete. Rather than getting the HD replaced in the Fusion Drive I would strong recommend getting an external SSD and making that your boot drive and primary drive. This is wise for several reasons:

• Less expensive than a repair bill from Apple.
• Will make the computer significantly quicker with a SSD.

To do the external SSD just follow the instructions in How to setup an external SSD as your startup disk and the external SSD I would recommend is the OWC Envoy Pro EX Thunderbolt 3.

If you do not feel competent to do the work then take it to your local Apple Authorized Service Provider and they should be able to do the work for a reasonable cost. Don't take it to an Apple Store (they won't do the work) or to the Best Buy Geek Squad, anyone else is fine.

Yeah' that's what I was afraid of.

Safe Mode may or may not help....

Use safe mode on your Mac - Apple Support

I would try Safe Mode, but then I would not use or use the iMac as little as possible until it is backed up.

There are other options beside Time Machine, like CarbonCopyCloner or SuperDuper for backing up.

https://bombich.com/ or https://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html

Sadly without a prior backup, it could be very difficult to backup and it may already be too late.

Plus running in Safe Mode will not allow you to use CarbonCopyCloner or SuperDuper.

Please keep us posted on your progress.

Glad to hear that you were able to make a backup. Now you are at liberty to have the drive replaced or replace it with a new Mac and then Migrate from the Time Machine backup. see > Transfer to a new Mac with Migration Assistant - Apple Support

To seek service for that older iMac, you may be forced to take it to an Apple Authorized Service Provider instead of an Apple Store. To find your local a service providers, go to > Find Locations and click on Explore Service Locations.

You're welcome.

If you find a loose or partially seated module, reseat all and test.

If not, then test with only the factory modules and then with only the Crucial modules.

Kernel Panics can be caused by hardware or software which can make them difficult to troubleshoot.

The next step is to check both drives that make up the Fusion Drive with DriveDX.

https://binaryfruit.com/drivedx

If both drives are healthy, then you will need to start looking at third-party software.