您可能缺少应用程序的开发配置。
在angular.json中，导航到architect-〉build-〉configurations，并在生产构建的定义下面添加以下行：

"configurations": {
  "production": {
    // already there!
  },
  "development": { // this is new!
    "buildOptimizer": false,
    "optimization": false,
    "vendorChunk": true,
    "extractLicenses": false,
    "sourceMap": true,
    "namedChunks": true
  }
},
"defaultConfiguration": "production"

要在开发模式下运行构建，只需键入下一个命令：ng build --configuration development .

顺便说一句：完整的工作配置（下文进一步说明），如果配置不是问题所在，则：

• 更新镶边，
• 删除并重新安装扩展
• （并允许在其配置中访问文件URL）
• 例如，以ng serve开头（如果是单一存储库npx nx serve <projectname>）

然后，您将看到类似的内容（取决于您自己的配置）：

** Angular Live Development Server is 
listening on localhost:4200, 
open your browser on http://localhost:4200/ **

• 在浏览器中打开
• 打开Chrome浏览器/火狐浏览器/.. DevTools
• 转到“Angular ”部分

您应该会看到：

最后但同样重要的是：完整配置示例：

{
  "$schema": "./node_modules/@angular/cli/lib/config/schema.json",
  "version": 1,
  "newProjectRoot": "projects",
  "projects": {
    "ng14.0.2": {
      "projectType": "application",
      "schematics": {
        "@schematics/angular:component": {
          "style": "scss"
        }
      },
      "root": "",
      "sourceRoot": "src",
      "prefix": "app",
      "architect": {
        "build": {
          "builder": "@angular-devkit/build-angular:browser",
          "options": {
            "outputPath": "dist/ng14.0.2",
            "index": "src/index.html",
            "main": "src/main.ts",
            "polyfills": "src/polyfills.ts",
            "tsConfig": "tsconfig.app.json",
            "inlineStyleLanguage": "scss",
            "assets": [
              "src/favicon.ico",
              "src/assets"
            ],
            "styles": [
              "src/styles.scss"
            ],
            "scripts": []
          },
          "configurations": {
            "production": {
              "budgets": [
                {
                  "type": "initial",
                  "maximumWarning": "500kb",
                  "maximumError": "1mb"
                },
                {
                  "type": "anyComponentStyle",
                  "maximumWarning": "2kb",
                  "maximumError": "4kb"
                }
              ],
              "fileReplacements": [
                {
                  "replace": "src/environments/environment.ts",
                  "with": "src/environments/environment.prod.ts"
                }
              ],
              "outputHashing": "all"
            },
            "development": {
              "buildOptimizer": false,
              "optimization": false,
              "vendorChunk": true,
              "extractLicenses": false,
              "sourceMap": true,
              "namedChunks": true
            }
          },
          "defaultConfiguration": "production"
        },
        "serve": {
          "builder": "@angular-devkit/build-angular:dev-server",
          "configurations": {
            "production": {
              "browserTarget": "ng14.0.2:build:production"
            },
            "development": {
              "browserTarget": "ng14.0.2:build:development"
            }
          },
          "defaultConfiguration": "development"
        },
        "extract-i18n": {
          "builder": "@angular-devkit/build-angular:extract-i18n",
          "options": {
            "browserTarget": "ng14.0.2:build"
          }
        },
        "test": {
          "builder": "@angular-devkit/build-angular:karma",
          "options": {
            "main": "src/test.ts",
            "polyfills": "src/polyfills.ts",
            "tsConfig": "tsconfig.spec.json",
            "karmaConfig": "karma.conf.js",
            "inlineStyleLanguage": "scss",
            "assets": [
              "src/favicon.ico",
              "src/assets"
            ],
            "styles": [
              "src/styles.scss"
            ],
            "scripts": []
          }
        }
      }
    }
  }
}

我在angular.json中有所有这些设置和配置。对我来说，问题如下：
main.ts:

if (environment.production) {
  enableProdMode(); // <-- here
}

platformBrowserDynamic()
  .bootstrapModule(AppModule)
  .catch(err => console.error(err));

显然，我在过去的某个时候更改了environment.ts文件的production属性，将其中的production设置为true，即使在开发模式下也是如此。
把它改回false终于为我解决了这个问题。