TapNoiseA connected display or dock can add an audio output to your Mac. If sound disappears or comes from the monitor after connecting it, inspect Sound › Output before changing the application.
Select the device you intend to hear
Open System Settings › Sound › Output and look for the monitor, HDMI connection, dock and built-in speakers. Choose the Mac speakers and play a known clip at a low volume.
A display can expose an audio route even when its speakers are absent, disabled or controlled elsewhere. The name appearing in the list is not proof that it will produce sound at the level you expect.
Check the display’s controls
Some digital outputs do not offer a working macOS volume slider. Use the monitor’s own volume or on-screen menu where appropriate. Avoid repeatedly pressing volume keys without checking which device owns the audio.
If only one app keeps using the display, inspect that app’s output selector. Conferencing and audio software can retain their own device choices.
Keep typing audio on the laptop
TapNoise’s Use MacBook speakers setting can keep its audio local even while your main output changes. That is useful for a docked laptop, provided speaker playback is suitable for the room.
For a complete path check, see switching Mac output devices. If no source works through internal speakers either, move to the wider silence checklist.
Sources: Apple’s output-device settings, TapNoise speaker routing.