Install https://github.com/RHVoice/RHVoice to get the text to speech service on graphene.
Came to the same conclusion. When I tried it out several years ago, it was also lacking text2speech, which is also provided by Google, so I did not even had voice announcements for routing. Not very pleasant.
You could give OrganicMaps a try. The routing is pretty decent: https://organicmaps.app/de/
Discussion
cool! will check it out, thanks