Hello Robert,
When using a RowTemplate, everything in the row must be implemented by the developer. This would include not only selection, but also things like detail templates, buttons and the like.
So, you would need to add a field in the model that denotes selection and bind the checkbox to it. If you want clicking the row to also invoke this, add an @onclick handler to the elements yourself that toggles this field as well.
Regards,
Marin Bratanov
Progress Telerik
UI for Blazor