macbookair 2014-15 model yosemite macos 10.10.5 external DELL HDMI monitor sound and brightness control I need to control brightness and sound volume in external monitor DELL 2420HS connected thru HDMI cable from thunderbolt port. I downloaded MonitorControl. image (dmg file) is showing 'corrupt image' when trying to open. Tried all versions starting 2.0.0...1.7.1, 1.7.0, thru to 1.5. The same error message. Please help.
Minimum OS requirement, according to the github page, is Sierra, macOS 10.12
A MacBook Air from 2014 is perfectly capable of running 10.15, Catalina.