Volume when using MacBook Pro 2019 with external monitor not working

leuyd3 Said:

”On the MBP the volume buttons gray out.”

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A. Reveal Your Installed Audio Devices:

If Nothing is revealed then fix the missing macOS Files. You can do so by either:

• restore Safari from a backup; or 
• reinstall the macOS

B. Set Up a Genius Bar Appointment. You would take your Mac, along with the adapter, the monitor and all else to your Local Apple Store. There, the audio and all other necessities would be looked at. These are third party items. So, contact Apple, and see if this is an option. Contacting Apple:

• Contact Us - Choose Locations
• USA: 1(800)MY-APPLE
• Proceed From there as Necessary

Is there a VGA connector on this monitor? If so, use this: USB-C VGA Multiport Adapter - Apple

Using a HDMI cable, your using Audio and Video on one cable.

So, use the VGA port, and all audio might just work.

lueyd3 Said:

”What's wrong is when playing a video there is no sound.”

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Reset the SMC and NVRAM:

Sometimes operations are performed and then the sound/speaker settings become manipulated, technically. So... Attempt resetting the SMC and NVRAM. That might just do the trick.

you do not need an Apple display.

But if you want help, you need to tell Readers what display you do have, and how you are connecting it to a Mac that only has Thunderbolt-3 ports.

what external device? what brand and type?

what type of cable are you using for the final connection?