Thanks for visiting the Apple Support Communities. From your post, I understand that when trying to get Target Display Mode working between a 2016 MacBook Pro and a 2011 iMac, pressing Command+F2 or Command+Fn+F2, nothing happens. I'm happy to help!
Reviewing the information in Use your iMac as a display with Target Display Mode - Apple Support, I see that your computers should be able to use Target Display Mode together, as long as you have the appropriate cables and adapters. Since you do, please utilize the steps below, taken from the above article:
If your iMac doesn't switch to Target Display Mode when you press Command-F2, check these things:
Make sure that the iMac you're trying to use as a display supports Target Display Mode.
Target Display Mode works only when your primary Mac is logged in to a macOS user account. For example, if your first Mac is at the FileVault login screen, pressing Command-F2 on your iMac does not enable Target Display Mode. You must first log in to your Mac (using a regular display, if necessary) before you can use an iMac in Target Display Mode.
Make sure that you're pressing Command-F2 on the keyboard that's connected to the iMac you want to use as a display.
In Keyboard System Preferences, if the checkbox is enabled for "Use all F1, F2, etc. keys as standard function keys," the key combination changes to Command-Fn-F2.
Make sure that your Mini DisplayPort or Thunderbolt cable is connected to both computers.
If you're currently logged in on the iMac you want to use as a display, try logging out to return to the login window. Then press Command-F2 again.
Some older Apple keyboards and third-party keyboards might not allow Command-F2 to toggle display modes. If this happens, use the keyboard that came with your iMac to toggle Target Display Mode on and off.
If your iMac is currently started up in Windows, it won't enter Target Display Mode. Target Display Mode isn't supported in Boot Camp.
Enjoy your weekend!