F keys not working
Why aren't my f keys working to adjust my brightness on the screen? The icon pops up when pushing them but nothing happens to the brightness. If I go into preferences I can manually adjust it but not with the f keys.
MacBook Air
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Make sure the F keys are not selected as function keys. > System Preferences > Keyboard > Keyboard > uncheck the Use F1, F2, etc, as standard function keys box, if that's been checked. That's probably not checked, given the graphic you're reporting appears when the brightness keys are pressed. But do confirm that.
Reboot the MacBook Air into Safe Mode, and reset both the SMC and NVRAM while you're rebooting into Safe Mode, and try again. Safe Mode disables various add-on packages—some add-ons have been known to cause weird problems—and rebuilds the boot caches and related. Then reboot normally, and see if that works better.
If that reboot back into normal operations should still have the problem with the function keys, upgrade to the most recent macOS High Sierra version if you're not already there, or upgrade to Mojave, and try again. I'd probably try loading the macOS High Sierra 10.13.6 combo update again, or the Mojave combo update. That should be harmless, but do have a backup.
If that fails, ring up the folks at Apple Support and ask about this.