I got a working solution, I replaced :

  "targets": {
    "build": {
      "executor": "@angular-devkit/build-angular:application",
      ...
    },
    "serve": {
      "executor": "@angular-devkit/build-angular:dev-server",
      ...
    },
  },

with:

  "targets": {
    "build": {
      "executor": "@nx/angular:application",
      ...
    },
    "serve": {
      "executor": "@nx/angular:dev-server",
      ...
    },
  },

in the project.json of the angular app