Rail Route from developer Bitrich is currently in Early Access and they just announced their plans for the big 1.0 release to happen on February 22nd. Rail Route has Native Linux support and is rated Steam Deck Playable and a demo is available too if you wish to try it first.
In the announcement they also mentioned they've crossed over 100,000 sales! It's been through some pretty huge improvements during Early Access across ~20 major updates. They've also confirmed more updates are planned to come after the 1.0 update.
With its minimalist design it may look quite simple and inviting, but it's quite a complicated beast once it gets going. Having to manage and automate many different train-lines is no simple task to get right, and you can end up sinking dozens of ours at a time into it. A really interesting building sim overall.
You get a lot of freedom with it too building up from scratch as you gradually unlock new tech and resources to build the ultimate rail network across real-world city maps. There's a lot of different ways to play it too, the choice is yours from getting everything running perfectly on time and just endless tweaking or high-pressure, time-sensitive scenarios.
You can buy it on:
GOG (coming soon)
One of the more recent update trailers is below showing off some new options: