It's not exactly the same, but Slay the Spire scratched some of the same itch for me. It's got the same meta-structure as FTL, but the fights use a deck-builder format. It's really well done.

One Step From Eden seemed like it should be even better for me, since it borrows the positional strategy stuff from the Mega Man Battle Network games, but I couldn't get into it. Mostly I remember it being just way too fast. I really wanted to like it, but basically didn't.

And yeah, as someone else mentioned, Advance Wars is good, too. The thing that Into the Breach did that Advance Wars didn't, for me, was that Advance Wars basically depended on the AI being a bit crap so that you could overcome an initial disadvantage and work up to victory. Into the Breach gets around that by making the enemy wholly predictable instead, which is arguably more fun. The only other game I know of that worked that way was an Android game called Auro, but I don't think that's playable anymore and I believe the dev has abandoned it. It's a shame, as it was really well made.

Other than that... you could try learning Go (aka igo, baduk, or weiqi). It's a board game with very simple rules, but very deep strategy that emerges from those rules. The main disadvantage is that it's multiplayer only, but there are puzzles, problems, and AIs you can use to turn it into a solo time killer.