@Koberg, Henrik (SMO SW MAAS COC-GER) Thanks for posting your question in Microsoft Q&A, apologize for any inconvenience caused on this.
I have followed the documentation steps and as you mentioned in step#6 document is suggesting to apply filter condition on field Title
which an non-filterable field and when I tried the search query got failed.
This seems to be a documentation issue, I will be sharing this feedback to the content author on this.
Hope this helps, let me know if you have any further questions on this.