Love your Tower Defense? You might want to keep an eye on Tau Cubis which will be releasing later this year.
With rather shiny graphics in a sci-fi / space environment, solo developer Cube Mandarine it's confirmed to be coming to Linux and they mentioned it will support both OpenGL and Vulkan on Linux. You can check out some early footage below:
The real-time pathfinding sounds like it could make things interesting. The developer mentioned that there's no pre-defined path for enemies to take, making each play-through totally dynamic so you can try to funnel them into a kill-zone of your own making as you build up your towers.
Each map will have several modes of play, and be solved in different ways and it sounds like each round won't take very long between 5-10 minutes so might be a good coffee-break tower defense. Additionally it will have leaderboards to see if you can beat others.
You can follow Tau Cubis on Steam.