Edgewise

Slide along your MacBook trackpad’s edges. Right edge for volume, left edge for brightness.

Free. macOS 13 or later, Apple silicon and Intel.

Download for Mac

macOS will say it can’t check the app for malware. Open System Settings › Privacy & Security and click Open Anyway, or skip that by installing from Terminal:

curl -fsSL https://edgewise.pages.dev/install | sh
Also: double-tap the top-right corner to mute, swipe the bottom edge to skip songs.
The Edgewise menu bar panel: brightness at 62 and volume at 44 shown on a trackpad map, with switches for haptics, quick mute and the media strip.