Version 1.2b does the job. My library is now scanned completely and i can listen to music. But unfortunately the program is very unresponsive during the scan and the scan takes ~30 min on my machine (>20K songs). In comparison: A scan in the official jellyfin player takes about 15 seconds. But the worst part is, that the library scan is done on every start. Maybe you can find a way, to speed this up?
Cheers