I think it's probably older than that, related to "cyberspace decks" in William Gibson's Neuromancer which was written in the early 80s on a 50-year-old mechanical typewriter.

Yes and then in the TTRPG Shadowrun

Cyberdecks were featured prominently in video game Cyberpunk 2077 - the 2020 and 2023 spikes may have been caused by that game, and the subsequent expansion.

fyi https://books.google.com/ngrams/graph?content=cyberdeck&year...

(I'd like to know who was using "cyberdeck" in 1976)

Ok, I see - it's a consequence of the smoothing function used in the graph. First actual use is 1979.