And I posted what I got from the Apple website today which shows my computer is compatible! Thanks for your comments!
I lost all Bluetooth capability on my 5K iMac after the install, but everything else is working okay. Tried to reinstall per Apple's instructions, but that wanted to take me back to Catalina so a no-go. Was told a "clean install" was my only remaining option, but have decided that is a bit too risky should something else not click.
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