The Unity UI package allows you to create in-game user interfaces fast and intuitively. This is an modified versions which allows you to setup multiple UIs controlled by separate users/inputs.
This package is in development, and requires Unity 2019.2.
The Unity UI user manual can be found here.
Several components found in the TextMeshPro package are using the EventSystem.current static property and would require modifications themselves to work with the MCU. This is scheduled for a later point and might be provided as per-component replacements or derived types to address the problem.