“Brightness Settings not Working on Mac Mini Intel 2018: Hi! My Mac Mini has been perfect, but during the past few weeks, I haven't been able to adjust my brightness using the slider or the keyboard. I also looked in the settings. Adaptive brightness isn't on. Any help would be great! Thanks!”
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If the Touchbar is Not Operating as it Should:
A. Reset the SMC and your NVRAM: Sometimes when changes are made to the system(i.e. updates) and then system configurations (i.e. for Screen Brightness) become manipulated, technically. So, reset the SMC and NVRAM
B. Boot in Safe Mode: [Hold Down: shift key, upon boot], In Safe Mode, Login Items do not run at login, certain preferences are set aside, and damaged system files are then reset. So, once booted in to Safe Mode, wait 30 seconds, and then boot up normally, attempting another update install.