KendoReact works under Linux, even some of our developers are using Linux to develop it.
The Start Free Trial is a static message and it is not connected to the active license. The team is working on fixing that as I completely understand that it is strange to see Start free trial when you already have a valid license.
Currently, no credentials are needed to use the component, the license is for legal reasons.
We had a private registry before but it created many inconveniences, and we made it available for download until we find a way to add the login step without making the process inconvenient for our users.
I can confirm that you have a valid license for KendoReact and can use it under Linux, Window, and macOS.