Mainframe Defenders released back in February 2020 is a quality turn-based tactics game with a very retrofuturistic visual style like old terminals and now there's a free Mainframe Defenders: Meltdown - Prologue to play.
Read the full article here: https://www.gamingonlinux.com/2021/06/mainframe-defenders-meltdown-prologue-gives-you-a-taste-of-the-excellent-tactical-game