Looking at your components for the first time and downloaded the 30 day trial today. I note in Visual Studio 2019 that you set <LangVersion> to 7.3 for each of the samples and the VS templates I've installed.
Is this a requirement to stay compatible with your package?
The big pull for us with C# 8 is nullable reference types. I suppose I can just turn it on and wait for Telerik components to be incompatible.