That article was showing PC but fortunately I had actually found that resolution about 2 hours after posting my question. For the next person's benefit, here's a screenshot of what is seen on the Mac. After going to the Printers tab in System Preferences you need to click on the "Options and Supplies" button and you'll see this:
Unfortunately, the Phaser 6510 does not send information to the Supplies section (of System Preferences - Printer) so it remains that if you are linked to USB you cannot see what the status is your toners are without going through the maze of pushing buttons on the top. It would be sooooo nice if this could be added to the otherwise wonderful Phaser printer.
And thank you for your help, I do appreciate it.
I searched our Support Page and found this article that says to make sure Duplex is installed from the driver options.
I have printed dobule sided documents many times before. However now, when accessing double-sided printing, the option is grayed out. This happens on any kind of document.
I have tried restarting and I've reinstalled the drivers for my printer, all to no change.
I'm on Mac OS 11.3.1. I using Printer drivers _5.7.2_2221.
Otherwise, it's performing just fine.
Any and all help is appreciated