I’m sorry to be not precise, I meant text to speech like the spoken directions using Magic Maps. These sound awful.
SherpaTTS packages a great improvement in speech engines: Alternative to eSpeak? - #46 by MRTN - can be set as Android system wide.
Magic Earth will use it via General → Sound → Voice Language - Text-to-speech (Android robot).
I wonder though what your settings were that you experienced as eighties-like, the App built-in engine or the Android system engine, the former did strike me as good enough (vs PicoTTS).