Unciv

This is a free, offline-playable turn-based strategy game that closely replicates the Civilization experience on mobile. It offers deep, complex gameplay that can be enjoyed in medium-length sessions, but is also highly interruptible and playable one-handed, making it suitable for quick breaks or longer engagements. With no monetization or energy timers, it's a great choice for players seeking a challenging yet relaxing strategy game with high replay value.