MacBook Pro FaceTime no sound output

Re: MacBook Pro FaceTime no sound output: I have tried all of the suggestions. Nothing changes. Zoom has sound. My speakers play online videos just fine.

We can not guess what suggestions you have already tried, so please excuse if you tried suggestions below.

Perhaps the first thing to check is whether your MacOS version is the newest compatible version for your Mac:

Identify your MacBook Pro model - Apple Support lists the newest compatible Mac OS for each model.

If still using MacOS 11.4 as your post suggests, and you want to continue using "Big Sur" OS:

Eg: What's new in the updates for macOS Big Sur - Apple Support

says the newest update was "macOS Big Sur 11.7.10

This update provides important security fixes and is recommended for all users."

(Please remember: it is always wise to back-up your Mac first if updating MacOS:

Also check:

Whether your Mac has around 50 Gb or more memory / storage space free in which to operate smoothly:

See used and available storage space on your Mac - Apple Support

If all above is OK already, and / or:

If you haven't seen and followed Apple Support's Troubleshooting article:

See their advice about microphones below:

If FaceTime isn't working on your Mac - Apple Support

Eg: says:

"If your camera or microphone doesn’t work

• Quit FaceTime, then open FaceTime again.
• Restart your Mac.
• Make sure that FaceTime isn't open, then see if your camera works in another app, such as Photo Booth. If it doesn't, you know it's not an issue with FaceTime.
• If you have multiple cameras or microphones connected to your Mac, check the Video menu in the FaceTime menu bar to make sure that you have the correct camera and microphone selected.
• If the issue involves your computer's built-in camera, learn how to resolve issues with the built-in camera.
• If the issue involves iPhone when used as a webcam, consult Continuity Camera: Use your iPhone as a webcam for Mac."

Other things to check: The speakers need to not be in use with another app when required for FaceTime.

Ensure they are not "muted" (audio-button crossed through)

VPN, ad-blockers, virus checkers, cleaners and the like can cause interference.

Try turning any un-necessary third-party apps off, or use uninstallers from developers.

Any third-party apps you find necessary need to be kept up-to-date for compatibility.