MakeMake a mesh gradient
The generator opens on the Mesh style. Pick two to six colours and a background, or start from one of the palettes above. Colour order matters: the first colour sits in the light and the last in the shadow, so put your lightest colour first.
Then shape it. Scale sets how large the colour fields are, Blur how softly they meet, and Warp how much they ripple into each other. Seed turns the direction the light comes from, and Speed sets how fast the colours drift. Add grain to take the digital smoothness off.