Light Block prevents the growth of many blocks

Light Block prevents the growth of

• amethyst from budding one
• sugar cane, bamboo, kelp, tree, mushroom
• big dripleaf
• grass, fern, seagrass
• glow lichen
• vines, cave vines, weeping vines, twisting vines
• chorus plant

It also prevents the growth of grass, flowers, corals by using bone meals on grass blocks/ under water in warm ocean. (It also prevents player using bone meals on these blocks.)

It doesn't prevent the growth of fungus.