My keyboard backlight is unadjustable, unusable (apparent software and/or firmware issue). What can I do to fix it?

The backlight on my keyboard for my 2019 MacBook Pro 15" is not adjustable and is always dark after my computer starts up. It does turn on (lights up to max. brightness) when I turn on or re-start my computer, suggesting that this is not a hardware issue. The touch bar (including backlighting) is working perfectly and keys on the keyboard all work. My touch bar and control centre still show the icons and slider bar, respectively, for adjusting keyboard brightness. Upon touching and clicking these options, respectively, the icons light up and slider bar slides but will not stay where i slide it to—it just jumps back to the off position. The keyboard brightness setting are completely absent from my system preferences (see screen grab below). Aside from the backlighting for the keys, my keyboard is working normally with zero issues.

Here's what I've tried so far:

• Ran hardware diagnostics and no errors were found
• Took it to the Apple store where they ran diagnostics and could not identify the cause of the problem
• Re-installed my operating system
• Installed a different operating system
• Read dozens of obscure blog posts trying to come up with any more ideas of things to try

Here are the two remaining avenues to pursue I can think of, both of which I'd like to avoid as they are rather incompatible with my traveling schedule for work:

• Completely wiping my computer and reinstalling it as a if it were a new computer, which I really want to avoid as it would take my computer out of commission when I need it for work.
• Get the keyboard replaced (what Apple has suggested), even though it seems to bee 100% fine aside from the inability to control the backlighting for the keys

Any advice or alternative suggestions for things to try and resolve this?

Thanks in advance.