Volume control via function keys stopped working

I have a 2015 MacBook Air recently updated to Mojave 10.14.6. The function keys used to allow me to change the volume (F11, F12) and screen brightness (F1, F2). These recently stopped working, maybe with the update? Now F11 triggers "show desktop" and F12 in Chrome opens developer tools.

Other functions stopped working years ago, notably F8, F7, F9 for play/pause, skip back, skip forward. But this is worse. I don't want to live without a keyboard shortcut for volume control.

In System Preferences>Keyboard>Shortcuts I have tried unchecking all the shortcuts of function keys. The result of this is F11 does not visibly do anything, and F12 still opens developer tools in Chrome. In System Preferences>Keyboard>Keyboard I have tried checking or unchecking "Use F1, F2, etc. keys as standard function keys." Results are the same whether this is checked or unchecked. My volume buttons are gone.