What will no doubt be a popular release, Warhammer 40,000: Mechanicus II from Bulwark Studios and Kasedo Games now has a demo available. The first game did have a Native Linux version, but this will not - so you'll need to run it with Proton on Linux systems.
More about Machanicus II: "After millennia of slumber, Vargard Nefershah mobilises her dynasty’s legions to annihilate the Adeptus Mechanicus interlopers who unknowingly settled upon her world. Across the galaxy, Magos Dominus Faustinius is summoned to bring his hard-won expertise to bear and ensure the Necrons do not succeed. The conflict soon becomes a crucible of unanticipated significance, drawing to it external actors stranger and more deadly still.
Two playable factions, two narrative campaigns, two highly unique play-styles and one important choice – who will you lead to victory in this arcane technological war of cold metal hatred?"
You can see the original gameplay overview from August below:

Direct Link
About what the demo will offer: For the very first time, players can experience the prologue of the game, where they will play as both the Adeptus Mechanicus, battling against the awakening of a Necron tomb world, and the Necrons, who strive for the resurgence of their dynasty.
The hands-on demo offers players a taste of the strategic gameplay that is again at the forefront of the action, with players able to assemble forces for each mission, choosing from a vastly expanded selection of fighters from each faction’s range. New environmental mechanics will also require players to maneuver their forces like never before and play to their chosen faction’s strengths and weaknesses - take cover behind terrain as the Mechanicus, or destroy it as the Necrons.
I will definitely skip this demo though and just wait for full release. I wanna go all in!