This invalid configuration you found in community documentation. If you are going to check that documentation, you would see that there is exists new official documentation, which you can found here Turris Documentation and it is mention in this thread:
Community asked is in the past for documentation, where they can add, edit and modify articles. So, feel free to register, and start writing.
VLANs requires some knowledge and that’s why you can setup it in LuCI and in CLI for now. We are using DSA since Turris OS 4.0 instead of swconfig and recently if I am not mistaken OpenWrt did the same change recently and without providing migration script and once they release a new version, you will be on your own if you would be using it.
There’s a way how to configure them and you will find it here: