OK, this printer, my Brother HL-3170CDW, had worked perfectly, without even having to install a driver.
Later, I did find the driver for this printer and installed it. I had to reinstall (faster than looking up an obscure problem), and, before I did anything else, installed the driver from the AUR.
I can see the printer (I did have to reinstall manjaro-printing twice before it appeared), but rather than recognizing the drivers already installed, game me the "Choose Driver" interface, in which, under Brother, HL-3170CDW does not appear.
The CUPS page doesn't even see the printer, with the CUPS drivers installed.
I tried the closest model number in the wizard, and got this when I tried a test page:
"Processing - Unable to locate printer "BRWD85DE26C5CDF". The print status window says "Processing - not connected?"
I have a shipping label which I must get printed, but it's, so far, not possible.
Both the laptop and the printer are on the same network, naturally. I also used a
I have uninstalled and reinstalled manjaro-printer 6 or 7 times, and it still does not appear.