I'm trying to figure out why you want to disable the internet on this, and which version of OS X you want to use. I probably am misunderstanding your needs or plan.? But if I were setting up a print server, I'd get an older machine that ran the version of OS X I preferred (perhaps a version before all the problems started cropping up with Presets, maybe Monterey? ). Probably a used Mac Mini. Turn off all automatic updates for OS and the printer.? I'd think getting an M4 would lock you into Sequoia or later - perhaps that's not a problem for you?
Then there are several ways to get things to the printer: file sharing either from or to the server, or printer sharing, or Air Drop, depending on your needs.
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