Reccuring Kernel Panic

Uninstall Bitdefender by following the developer's instructions. Anti-virus apps, cleaning apps, and third party security software are not needed on a Mac and usually causes more problems than they solve plus they impact system performance.

If you still have Kernel Panics after uninstalling these types of apps, then run EtreCheck and post the report here using the "Additional Text" icon which looks like a piece of paper.

You can also run the Apple Diagnostics to see if any hardware issues are detected.

Uninstall Adobe Flash Player. It's outdated, obsolete and a know problem.

Visit the adobe website for a proper uninstaller.:

https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html

See if the problem still happens in Safe mode.

How to use safe mode on your Mac - Apple Support 

Does the problem persist while in Safe mode? 

Exit safe mode by restarting your Mac normally and re-evaluate the issue again after a normal reboot

If @D.I. Johnson's suggestion to boot into Safe Mode still results in a Kernel Panic, then try the following:

Run Disk Utility Fist Aid on the hidden Container. Within Disk Utility you need to click "View" and select "Show All Devices" so that the hidden Container appears on the left pane of Disk Utility. Even if First Aid shows everything is "Ok" click "Show Details" and manually look back through the report looking for any unfixed errors. If there are any unfixed errors listed you will need to erase the whole Fusion Drive and restore from a backup or clone.

Check the health of the hard drive & SSD by running DriveDx and posting the reports here using the "Additional Text" icon which looks like a piece of paper. The report for the hard drive is most important.

How long have you had the memory upgrade installed and what is the brand of the memory? Perhaps one of the memory modules is bad or they may not be compatible with this Mac. Macs are very particular about the memory they use so it is best to only use memory from Crucial or OWC.

It looks like there is an issue with the file system and since First Aid cannot repair it you will need to erase the whole Fusion Drive and restore from a backup or clone. In order to be able to see and select the Fusion Drive within Disk Utility you may need to click on "View" and select "Show All Devices" so that the physical drives and Fusion Drive appear on the left pane of Disk Utility. You will need to erase the whole Fusion Drive as GUID partition and APFS (top option). A bad file system can definitely cause major system issues.

Before doing that though you need to provide the DriveDx report for the hard drive so we can be sure the hard drive is healthy. There is no sense going to all this work if the physical hard drive is failing. Unfortunately you only provided the DriveDx report for the SSD. You will need to click on the hard drive icon within DriveDx before clicking on the "Save Report" button.

That is very odd how the physical drives appear within DriveDx with your Fusion Drive setup. However, the hard drive does appear to be healthy with no obvious signs of problems.

I would say the next step is to address the file system issues. Since your iMac is using the HFS+ file system you actually have two options. One is to pay for the Disk Warrior utility to attempt to repair the file system of the Fusion Drive. While Disk Warrior is really good at repairing HFS+ volumes there is no guarantee it will be successful. The other option is to perform a clean install of macOS by first erasing the whole Fusion Drive as GUID partition and MacOS Extended (Journaled) before installing macOS. During the initial boot of the new clean OS you will be offered a chance to restore from a Time Machine backup. The choice is yours on which option to try. The second option when done correctly will definitely resolve the file system issues, but it does involve a lot of extra work and time.

Keep in mind there is no way to know whether the file system issues are the only problem with your iMac. It is the next logical step since we know there is an issue with the file system.

If you go with option two it would be a good idea to test the system for a bit before migrating from the backup since if a clean install has Kernel Panics it means your iMac has a hardware issue of some sort.

No matter which option you choose make sure to have a good backup before doing anything else.