Kernal Panic on iMac During Sleep

Kernel panics are caused predominately by hardware faults and third-party kernel extensions.

You don't have any third-party kernel extensions, so the cause is most likely hardware. There are a few other rare conditions that might generate a KP, but the only one I can remember is NVRAM. So, you can try an NVRAM reset, but I wouldn't get my hopes up.

The panic may have something to do with WiFi, but that isn't in any way conclusive. Do you connect via WiFi or Ethernet cable? If a cable, are you using an USB Ethernet adaptor?

Did you get referred to Best Buy from the Apple Support site, listing them as an Authorized Repair center?

You might take a copy of the panic log to the repair center and see if they can run specific tests that may not have been run the first time.

The only Apps that I installed after reinstalling macOS are:

-Firefox

-Dropbox

Apps, in and of themselves, do not cause kernel panics. If the app installs a kernel extension, then that might be a possibility, but as I stated, you don't have any loaded in the panic log.

I would never trust Best Buy with much of anything. I was just trying to confirm that they are an Authorized Repair Center. If they are not, and you were just referred there because it is the next best thing, then they probably won't be able to conduct the necessary tests to find obscure hardware faults that would cause a kernel panic.

They may have just run Apple Diagnostics like you did. It won't find much.