Given these plugin repositories:

pluginRepositories {
  maven {
    url 'my-company-repo'
  }
  gradlePluginPortal()
}

When a plugin from the company-repo depends on another plugin from the plugin portal, it cannot be resolved.

The workaround is to explicitly add the plugin portal maven repository as another plugin repository:

pluginRepositories {
  maven {
    url 'my-company-repo'
  }
  gradlePluginPortal()
  maven {
    url 'https://plugins.gradle.org/m2'
  }
}