In the Help documentation page "Painting Brush Strokes" - online and macOS Help file - the modifier key for changing flow is given as "press the ⌘ key then a number key":
In fact the modifier to change flow is the ^(ctrl) key together with a number (not sequentially, as possibly implied by "then"). ⌘ with a number (0, 1, 2, 3, 4, 8, 9) modifies the view magnification.
Cheers,
H