What does the Vivid app do and how does it work on macOS?

Vivid opens the brightness range macOS keeps locked on a MacBook Pro 14"/16" or Pro Display XDR (about 1,600 nits, system-wide). It uses the headroom Apple reserves for HDR video, the same way an HDR clip pushes the panel brighter. It runs on the keys you already press, so they go roughly twice as bright everywhere, not only in HDR content. It's a one-time purchase, no subscription, on Apple's own frameworks. MacBrightness does that same core job for $5, where Vivid is the best-known original at a higher price. Neither helps a MacBook Air, Intel Mac, M1 13", or Studio Display; those panels are already at true max.