我已经设法解决它添加以下行：

in ConfigureServices

if (HostingEnvironment.IsProduction())
{
   services.AddSpaStaticFiles(configuration =>
 configuration.RootPath ="ClientApp");
}

in Configure
                app.UseHttpsRedirection();
                app.UseRouting();
                app.UseAuthentication();
                app.UseAuthorization();
                app.UseEndpoints(endpoints =>
                {
                    endpoints.MapControllers();
                });
                if (env.IsProduction())
                {
                    app.UseSpaStaticFiles();
                    app.UseSpa(spa =>
                    {
                        spa.Options.DefaultPage = "/index.html";
                    });

我在.NET 6中通过以下方式实现了这一点：
1 -使用package.json中的postbuild步骤，将React应用程序的生产版本复制到Web API wwwroot文件夹

"scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "postbuild": "move build ../YourWebAPIProject/wwwroot",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },

2 -更新了Web API项目中的program.cs，以包含以下内容

app.UseRouting();
app.UseDefaultFiles();
app.UseStaticFiles();

app.UseAuthentication();
app.UseAuthorization();

app.UseEndpoints(config => 
{
    config.MapControllers();
    config.MapFallbackToController("Index", "Fallback");
});

3 -添加回退控制器以处理响应路由

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;

namespace YourNameSpace
{
    [AllowAnonymous]
    public class FallbackController : Controller
    {
        public IActionResult Index()
        {
            return PhysicalFile(
                Path.Combine(
                    Directory.GetCurrentDirectory(), "wwwroot", "index.html"), 
                    "text/HTML");
        }
    }
}

这种方法允许WebAPI和React路由都工作，由WebAPI项目提供服务。
希望这对某人有用