That little person icon indicates you've got an accessibility feature enabled - like the shortcut button at the bottom right of your screenshot. It might be the "Select to Speak" feature, perhaps? (Or, at least, enabling "Select to Speak" on my phone got the dual volume controls shown in your screenshot. There may be others that result in the same thing.)

Take a look at Settings > Accessibility and turn off anything you're not actively using.

 

Google has a pretty extensive collection of articles in various Help Centers:

• Pixel Phone Help
• Android Help
• Android Accessibility Help

I don't think it would be feasible for them to document everything given the pace at which features change, but those should at least provide a start.

Here's an article on the Sound Amplifier, though I don't think it directly addresses the dual volume controls:
https://support.google.com/accessibility/android/answer/9157755

 

I'm glad I could help! Those Help Centers also have communities attached with Pixel/Android experts standing by to help out if you run into any issues or questions that don't get handled here at Android Forums.