What it does
While you play, a game builds shaders, the small programs your Mac’s graphics chip runs, and the engine notes which ones it needs. Malbec prepares those for the next session after the game has closed, in the background: when the Mac is on its power adapter or hasn’t been used for a while, never while a game runs, in Low Power Mode or when the Mac is hot. It shows in Activity. It runs at low priority. Pressing Play stops it at once; what it finished is kept. Before the game starts, Malbec gives what is left at most 5 seconds, and anything still left waits for the next quiet moment.
How to use it
Nothing to do. To start over, Clear… in Settings › Shaders removes a store’s shaders: it sets the folder aside first, so it is never left half deleted. The first sessions after that can stutter while the shaders are built again.