<RadzenTabs>
    <Tabs>
        <RadzenTabsItem Text="Tab1">
            Tab1
            <RadzenButton Text="Enable/disable second tab" Click="@(args => disabled = !disabled)" />
        </RadzenTabsItem>
        <RadzenTabsItem Text="Tab2" Disabled=@disabled>
            Tab2
        </RadzenTabsItem>
    </Tabs>
</RadzenTabs>

@code {
    bool disabled = true;
}