9 Kings is a fast-paced roguelike kingdom builder where you get to watch tiny armies fight and it's surprisingly absorbing of your time. Note: personal purchase.
This is not a kingdom / city builder like you may think. It's nothing like say Manor Lords, Crusader Kings, Civilization or anything resembling any of them. It blends in a weird mixture of a kingdom builder, with semi-auto battling and a sort-of deck-builder into something that just isn't like anything else.
You pick a king and then get given a plot of land to place your castle. From there, you have only a few squares to place down cards which form units and buildings to begin building your army. Each turn an enemy king sends their army to fight you, and the battles are mostly automatic apart from you using your castle ability (like throwing a big rock or lightning bolts) as units fight automatically on the field. It's a tug of war game, as you repeatedly expand your little kingdom gradually with more squares to place things down and power up your armies with various cards, to keep up with the next little invasion from an enemy king.
It's very much another numbers-go-up type of experience. One where you build up the most insanely overpowered combination that you can, while also getting to watch little pixel people get crushed.
The game just goes on and on and on with each turn being a year, while you pick new cards and upgrades and eventually you'll have amassed a ridiculous assortment of troops of all kinds. From standard soldiers to flying demons there's a lot of variety in how you build your little pixel army. Eventually you come up against the boss battle and if you win it's game over, or you can choose to play endlessly with a warning how it's "experimental" so there will be issues.
As you progress you unlock more kings, each with a different set of cards for buildings and units. You can also level up each king, to put points into meta-progression perks like unlocking more plots at the start to build on or levelling up your castle to higher levels.

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Another game that's very accessible too, since you pretty much only use the mouse and a single button. And especially nice is that each year (turn) you can just save, quit and come back to it anytime. Great for busy people and people with hours to spare alike.
It's in Early Access, and in my time playing it, there's been a few bugs that have forced me to reload it but it saves often so not a big problem. Hopefully as development goes on they can ensure it's stable. I've seen various reports from others on the same, so it's not Linux specific. Otherwise, it works just fine with the latest Proton 9.0-4 on Desktop Linux.
A tentative recommendation because it's enjoyable but a little unstable and the balance needs constant work as they add more to it. I really like it though and think you will too. Now if you'll excuse me my kingdom needs me. Time for another run.