There are currently compatibility issues with Unity 2019.3.0a6 and FMOD when we created a build for Linux. We moved to 2019.3 to fix certain graphical issues related to a change made in Unity 2019.1. However, being in any "non-stable" branches of Unity unfortunately causes Linux builds with FMOD integration to fail. We found that 2019.2 (the current stable branch) does work with FMOD on Linux. We worked with the Linux Game Consortium and found the best solution was to wait for Unity to make a stable branch.
In the future, it might be possible to make an official Linux Build through the 2019.2 version of Unity, though we are still doing testing on this front when we can. It is entirely possible that this testing will coincide with the Time of Creation update content. At that point, the Linux version could be released when Time of Creation is officially released.
Thanks for playing the demo! Hopefully that clarifies the state of Linux development.