Yea, it's a tough itch to scratch, for sure. I only have suggestions for games that have similar mechanics, but nothing that could be considered a straight up replacement for XCOM2.

• Battle for Wesnoth. Open-source, been around almost as long as the XCOM franchise, and very similar but in a fantasy setting and 2D with hexagonal grids. You can train new soldiers, or level-up veterans. They can die and you lose all your spent resources on them, etc. Loads of community made campaigns, too.
• Wasteland 1/2/3. Out of all of these, this is probably the closest to aesthetics and mechanics, but not entirely the same thing.
• Baldur's Gate 3. Obviously more fantasy and diff rules, but the combat is close enough at higher levels of difficulty.
• Divinity Original Sin 2. Uses action point economy, but otherwise like BG3. Combat is close.
• Expeditions: Rome. There are other Expeditions games, but this is the latest. A bit closer to XCOM I think, but in a historical setting.
• Into The Breach. Not exactly the same, but not entirely different either. Different gameplay focus but all turn-based on a grid with RPG elements in between battles to level up your squad.