Hi there! My name is David. It’s a pleasure to help you today.
Thank you for posting your question.
Did the sound on your monitor work fine before in the applications?
Check that Monitor is the Default audio output:
Go to the taskbar, on the right side right‑click the sound icon > Sound settings > There check that the audio output device is the monitor, it should say Dell (High Definition/Audio, Display audio).
Check the Volume Mixer for the applications (YouTube, Spotify):
Go to the taskbar, on the right side right‑click the sound icon > Open Volume Mixer > There look for the applications and make sure they have volume.
Also, you can check the audio output device for each application > Click the arrow next to the volume bar > and check the output device.
Let me know if the shared information has been helpful. Regards