BIG SUR BRICKED MY MACBOOK PRO

Apple's officially supported for Hardware is here:

MacBook Air (2013 or later) [Machine ID 6,1 shipped with 10.8.4, has to be upgraded to Mavericks 10.9 first

if you saved it in your App Store, or 10.12 from the App Store & have 35 GB free after the upgrade first before installing Big Sur.]

MacBook (2015 or later) [Machine ID 8,1 shipped with 10.10.2]

MacBook Pro (Late 2013 or later) [Machine 11,1 shipped with 10.9]

Mac mini (2014 or later) [Machine ID 7,1 shipped 10.9]

iMac (2014 or later) [Machine ID 14,4 shipped with 10.9.3]

iMac Pro (2017 or later) [Machine ID 1,1 shipped with 10.13.2]

Mac Pro (2013 or later) [Machine ID 9,1 shipped with 10.9.1]

dwb has a good point. And you can always override the internal keyboard entry with an external USB keyboard.

If possible, get to the username field and test the case of the typed character.

You can also see if the recovery mode, command-R works, and that will bring up in the menu the Terminal and see if you are typing all uppercase, or not. That will verify the case.

A Late 2011 MacBook does not support Big Sur. If you attempted to install it on unsupported hardware, don't complain about what was not designed to work.

Bypassing Apple's standard upgrade routine invariably leads to failure.

This is a stab in the dark - take a look at the caps lock key. Maybe you are inadvertently typing in all caps