They're props, but the design is based on a real terminal screen/keyboard from the 70's
The entire design premise of the show is based on an uncertainty of where we are in time.
"We wanted to confuse the viewer about whether this is a period piece, contemporary, or the future."
The "Lumon Industries" terminals are based on the Data General Dasher
D2 or D3 terminals (circa 1977/1979), but, according to production
designer Jeremy Hindle and set decorator Andrew Baseman, "any single
brand of computer would be too identifiable for viewers".
“We brought in every imaginable desktop we could think of. [...] We
made a computer that, if it ever came out in the real world and the
engineers described what they were doing, no one would believe them.
It’s a cathode-ray tube, but it’s a touchscreen. It has a trackball.
We recognize some aspects of it, and some not at all.”
The contradictory qualities are supposed to be baffling but also a bit amusing. “It doesn’t look like an adult high-tech computer,” Baseman added. “It looks like a toy.”
Quote from Keyboard Builders' Digest / Keyboard Spotting - Severance terminal itself quoted from Vulture - The Stories Behind Severance’s Eerie Office Design
I chose this particular one because underneath it has…
u/gza-genius posted some photos with the title:
My buddy made the keyboards in Apple TV’s “Severence”


…and as some else noted, "There's no Escape." Quite fitting.
Original Dasher D2, for comparison…
