Hi,
Nice to meet you! My name is Randy and I'm an independent advisor.
In Windows 10, the old "advanced volume control" for the Microsoft GS Wavetable Synth was removed, so you won’t find that slider anymore. To fix playback in Sibelius 2019, first check Play > Setup > Playback Devices and ensure the Microsoft GS Wavetable Synth (or another sound library) is enabled. Then, use Sibelius’s built-in mixer (M) to raise the master fader or adjust instrument levels. If there’s still no sound, open the Windows Volume Mixer while Sibelius is playing and raise Sibelius’s app volume. For better sound and more control, consider switching from the GS Wavetable Synth to the included Sibelius Sounds or a VST plugin.
Kind regards,