From the looks of that FAQ, macOS support for the project was effectively abandoned long ago. The most recent looking FAQ entries reference Mac OS 10.5, which was released in 2007. Declaring it "formally deprecated" now is - well, a formality.
(Is Gutenprint even relevant anymore? I don't know a lot about professional printing - if you know more than I do, how outdated does the printer list at https://gimp-print.sourceforge.io/p_Supported_Printers.php look?)
I think stopping binary releases is more than a formality though.
The last release was in 2019. For all intents and purposes, they'd already stopped.