First, thank you for all of your diligence and suggestions on how to get this file OFF of my iMac. I'm happy to report: Mission Accomplished. How?
The link you provided to "thexlab..." suggested a number of native OS solutions (which didn't remediate the issue), but it did two utilities: Trash It! and Cocktail. I started with Trash It! (no bueno) then went on to Cocktail, which has a Big Sur compatible version. Eureka!
I had to disable the System Integrity Protection using the Recovery OS to allow the app to work it's magic (subsequently restored), but the file is GONE ... or at least no longer viewable to me. My guess is artifacts exist somewhere on the hard drive, but the immediate problem is gone.
Thanks again for your ideas and recommendations. I'm going to ignore a couple of them long-term (I'm a believer in VPN's and anti-virus software), but the acquisition of some very helpful utilities is now part of the repertoire and will prove useful in ensuring optional operation of my iMac going forward.