kernal panics and beachballing

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Hard drive too slow - The hard drive in this computer is too slow.

The reason your iMac is slow is due to the 5400-rpm hard drive. While this hard drive found in your Mac is perfectly suited to light tasks, such as email, web browsing, etc., for more advanced tasks, and for users who want the maximum performance from their Mac, this hard drive does have its limitations. Luckily, you can use an external SSD as your startup disk to run macOS and all your data from that. It will make your Mac 10 to 30 times faster for storage, and in turn, make your entire Mac system much faster. For more info, instructions, and what external SSD to buy, please see: How to Setup and Use an External SSD as your Startup Disk on a Desktop Mac - Apple Community.

Another option is to replace this Mac with a new Apple Silicon Mac: Mac - Apple. If you go this route, it is generally recommended that you purchase 16GB of Memory with the largest SSD that you can afford. You can also use Apple Trade-In to get credit towards a new Mac: Apple Trade In - Apple.

Also;

/Applications/ExpressVPN.app/

Delete Express VPN. Mac computers do not need any sort of anti-virus, cleaners, VPNs, etc. The only thing they are good at is creating false marketing promises and taking consumers' money. They are all scams. In fact, anti-virus and other cleaners cause performance issues, security issues, and make macOS appear buggy. Your Mac is far worse with these types of Apps installed.

Mac computers have protection built-in, which is the best protection for your Mac. For specifics on macOS Security, see: macOS - Security - Apple and Protecting against malware in macOS - Apple Support. Mac computers also have built-in storage recommendations: Optimize storage space on your Mac - Apple Support. You can even use the built-in macOS Firewall: Block connections to your Mac with a firewall - Apple Support. Other than that, all you should do is restart your Mac approximately once a week and keep macOS up to date: Update macOS on Mac - Apple Support. 

However, should you ever get adware or malware on your Mac, the only tool that should be used to remove it is the free Malwarebytes for Mac. This App is the only exception to the general rule that no anti-virus, anti-malware, etc. should be used.

Jack

The EtreCheck report also shows you are using a USB2 hub. You should be using a powered USB3 hub which supports the UASP protocol for the best speeds of your external drives and devices especially if you will be booting from an external macOS drive connected to a hub.

You may also want to disconnect all the external devices in case one of them is causing a problem. Also try booting into Safe Mode to see if that stops the Kernel Panics or improves performance.

Try running the Apple Diagnostics to see if any hardware issues are detected. Unfortunately the diagnostics don't detect all drive failures so you may want to run DriveDx to check the health of the hard drive and post the report here using the "Additional Text" icon which looks like a piece of paper. However, like @Jack-19 says the original hard drive is slow even when it was brand new and healthy so booting from an external USB3 SSD will improve performance as long as the internal drive is not interfering (it can interfere with some types of drive failures).

You may want to run Disk Utility First Aid on the hidden Container. Within Disk Utility you may 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 says everything is "Ok" click "Show Details" and manually scroll back through the report to see if any unfixed errors are listed. If there are any unfixed errors listed, then you can try running First Aid from Recovery Mode, otherwise you will need to erase the whole physical drive before restoring from a backup or clone.