How do you set the check state to the checkbox programmatically?

You can check/uncheck the checkbox in the Blazor programmatically by using the @bind parameter in the checkbox. Assign a Boolean property to @bind in the checkbox and toggle the Boolean property programmatically.

@page 
<input type="checkbox" @bind="@boolvalue" />
<br />
Checkbox: @val
<br />
<button class="btn btn-primary" @onclick="@ToggleCheckbox ">toggle</button>

@code {

public bool boolvalue { get; set; }
public string val;
 void ToggleCheckbox()
 {
        if (boolvalue)
        {
            val = "unchecked";
        }
        else
        {
            val = "checked";
        }
        boolvalue = !boolvalue;
}
}