Requirements
Unity Version
The package has been fully tested in many Unity versions, but it's currently developed using Unity 2019.4 LTS. The package supports all versions from Unity 5.6 to Unity 6 (including yearly releases in between, e.g. 2018.4 LTS, and others).
Higher Unity versions should also work without any major issues. If any fixes are required for future versions, new updates will be released along feature complete Unity versions. Alpha and Beta Unity versions (.a & .b) are not continuously supported, and any issues found on them will only be addressed on full releases.
Older Unity versions (namely Unity 5.5 or lower) are not supported. There is no reason to believe that moderately recent versions shouldn't work, but changes in Unity's API may break the package.
Important
Some Unity versions may have some missing features. The package targets 2018.4 LTS as the base version, with lower versions being supported as "legacy".
The documentation marks which features are not available.
System Requirements
Unity Editor
Any system that can run the Unity Editor supports all features of this package.
Keep in mind that there is no official support for Stream Deck hardware under Linux. There are multiple open-source projects that aim to support Stream Deck hardware under Linux, but none of them support Stream Deck Plugins, which is required for the package to communicate with a Stream Deck.
Built project
Similar to Editor support, only Windows and MacOS built projects are supported by default, as this is a limitation based on Stream Deck's supported platforms.
Network
The package uses the port 2245 to establish an internal communication between the Unity Editor or built project and the Stream Deck official software.
There is currently no support to change this port manually, so if any other process is occupying the port, the plugin won't be able to initialise.