For me this solution worked.

On my github here : https://github.com/raphadesa/BlazorSSR

@page "/"
@inject IHttpContextAccessor HttpContextAccessor
@inject NavigationManager navigationManager 
@using Newtonsoft.Json.Linq
<HeadContent>
    <script src="https://www.google.com/recaptcha/api.js" async defer></script>
</HeadContent>
<EditForm @ref=Form Enhance Model="ContactModel" OnSubmit="HandleSubmitAsync" FormName="contactForm">
        <DataAnnotationsValidator/>            
            <div class="mb-3">
           <label class="form-label">Nombre:</label>
        <InputText class="form-control" @bind-Value="@ContactModel.Name" />
        <ValidationMessage For="@(() => ContactModel.Name)" />
            </div>    
    <div class="g-recaptcha" data-sitekey="you-sitekey" data-permanent></div>
             <input type="hidden" name="g-recaptcha-response"  />
        <ValidationMessage For="@(() => ContactModel.IsRecaptchaValid)" />
            <button type="submit" class="btn btn-primary">Enviar</button>
       
</EditForm>
@code{
    [SupplyParameterFromForm]
    Contact ContactModel { get; set; } = new();
    private EditForm Form { get; set; }
    HttpRequest httpRequest => HttpContextAccessor.HttpContext?.Request;    

    async Task<bool> validateCapcha(string response)
    {
        var secretKey = "you-secret-key";
        var apiUrl = "https://www.google.com/recaptcha/api/siteverify?secret={0}&response={1}";
        var requestUri = string.Format(apiUrl, secretKey, response);
        var http = new HttpClient();
        var request  = await http.GetStringAsync(requestUri);
        JObject jResponse = JObject.Parse(request);
        var isSuccess = jResponse.Value<bool>("success");
        return isSuccess;
    }

    async Task HandleSubmitAsync()
    {
        var response = httpRequest.Form["g-recaptcha-response"];
        ContactModel.IsRecaptchaValid = await validateCapcha(response);
        if(Form.EditContext.Validate())
        {   
            navigationManager.NavigateTo("Weather");            
        }
    }

}