Using Sierra App switcher, how do I get the app icons to display across the screen like in El Capitan so that I can tab to my desired app?

The Application Switcher goes way, way back. At least to Tiger, if not before. Unfortunately Apple only makes mention of it by name, while not explaining it in any detail whatsoever. For example, read "Quickly switch between apps" in OS X El Capitan: Window basics.

There are no settings for it, but it is conceivable that another Mission Control related setting, or perhaps an Accessibility keyboard setting is preventing it from appearing. Look into those possible causes.

Please determine if the same problems occur in "Safe Mode": Use safe mode to isolate issues with your Mac - Apple Support.

I do, but it also works normally and always had since it was introduced many years ago. I suggest you might try the following in order until the problem is fixed:

1. Restart the computer.
2. Reset your Mac's PRAM and NVRAM.
3. Reset the System Management Controller (SMC) on your Mac - Apple Support.
4. Boot into Safe Mode then reboot normally. Test in both states.
5. Create a new admin user account. Log into the new account. Does it work then?
6. Reinstall Sierra or El Capitan Without Erasing Drive:

Please be sure you back up.

1. Restart the computer. Immediately after the chime hold down the Command and R keys until the Utility Menu appears.
2. Select Disk Utility and click on the Continue button.
3. Select the indented (usually, Macintosh HD) volume entry from the side list.
4. Click on the First Aid icon in the toolbar. Wait until the Done button activates, then click on it.
5. Quit Disk Utility and return to the Utility Menu.
6. Select Reinstall OS X and click on the Continue button.

Does for me

There is no difference in the way the application switcher works in Sierra vs El Capitan.

As John said, restart in Safe Mode and test.

Great! Thanks for the update.