X-COM games in order
There are 7 X-COM games on sale here, from X-COM: UFO Defense (1994) to XCOM: Chimera Squad (2020), in the order each first came out. 2K published 4 of them. It lists the games on sale now, not every game ever made. Only keys and codes their shop says work on a UK account set a price.
Each price counts the fees its shop's feed gives. Some shops add a fee for some ways to pay. Some pay us when you buy through these links, which never changes the order. How that works.
X-COM: UFO Defense1994 · Steam£0.532 shops
X-COM: Terror From the Deep1995 · Steam£0.592 shops
X-COM: Enforcer2001 · Steam£0.592 shops
XCOM: Enemy Unknown2012 · Steam£0.762 shops
The Bureau: XCOM Declassified2013 · Steam£1.143 shops
XCOM 22016 · Steam, Xbox, GOG£2.903 shops
XCOM: Chimera Squad2020 · Steam£1.453 shops