I noticed that after the change to OH4 VoiceRSS is working, however the cache folder (/var/lib/openhab/voicerss/cache/ ) stays empty.
Writing onto that folder is possible.
Setting the bundle to DEBUG I get:
2023-07-31 17:54:20.291 [DEBUG] [voicerss.internal.VoiceRSSTTSService] - Synthesize 'Das ist eine Test.' for voice 'voicerss:deDE' in format AudioFormat [codec=PCM_SIGNED, container=WAVE, bigEndian=false, bitDepth=16, bitRate=256000, frequency=16000, channels=1] 2023-07-31 17:54:20.292 [DEBUG] [voicerss.internal.VoiceRSSTTSService] - Use common TTS cache mechanism
According the last entry I would have expected entries in the above folder!