Hello lindafromfolsom,
Welcome to the Apple Support Communities. I understand you're finding your volume keys aren't changing the volume, and I'm happy to help out.
Checking your Function key settings was a great start. You mentioned this is happening in Safari. Does the same thing happen in another app with audio, like iTunes?
Which Mac model and exact macOS version are you running currently? You can check the version under Apple menu () > About This Mac.
Is this a built-in keyboard, or external?
When you press F10 and F11, does anything happen at all? How about if you test by going into System Preferences > Keyboard > Keyboard and checking the "Use F1, F2..." box? When you do that and press F10 and F11, does anything happen? Testing in this way would help rule out possible issues with those specific keys.
Also, do other functions of your top keys, like adjusting the brightness, seem to work as expected?
Knowing the answers to those questions will help get to the bottom of this issue. Another step I recommend is testing to see if you can replicate the same issue in a temporary administrator account. This would determine if you have a system-wide issue, or if it might be user account-specific. Here's how to set up the temporary user and then use it for testing: How to test an issue in another user account on your Mac
I hope this helps get you started.
Take care.