While Firaxis is presumably busy working on the rumored turn-based Marvel game, a studio called Iridium Starfish has soft-launched an official XCOM spin-off on the Google Play store (opens in new tab). XCOM: Legends is still in development and only available in some territories, but gameplay footage is showing up on YouTube already.
The first thing to note about XCOM: Legends is that it's played vertically, and the second that, while it is turn-based, the only movement or positioning involved is deciding which of your heroes to put behind cover as they rush from one five-on-five encounter to the next. Also, repositioning has a five-turn cooldown.
XCOM: Legends is set in the XCOM 2 timeline, and has various familiar faces of the resistance pop up between missions. During the tutorial you discover an alien device called the Archway. What does this powerful psionic tech do? It lets you summon legendary heroes or artifacts in exchange for premium currency. XCOM: Legends is a gacha game where you supplement your regular squaddies with more powerful premade characters.
When you're not playing, gear and resources from the battlefield are collected by the "Integrated Drone Looting Experience", or IDLE for short. Just typing this sentence has made me feel deep-down tired in my bones.
Of course, if you want an XCOM game on mobile both XCOM: Enemy Within (opens in new tab) and XCOM 2 (opens in new tab) are already available, as are plenty of other neat turn-based games like Hoplite (opens in new tab).