Q.Why are hosta leaves turning brown?
Some hosta’s leaves are brown even when they’re unfolding! Why?

Root rot is also caused by a fungus, but it's most common in overly wet soil. The roots begin to suffocate in the waterlogged ground, causing the crown of the plant to become more susceptible to rot and the leaves to begin drying along their margins. Pull the mulch back so the soggy soil can dry and reduce watering temporarily. If the plant recovers, prune off the damaged leaves to improve the plant's appearance.
Root rot is also caused by a fungus, but it's most common in overly wet soil. The roots begin to suffocate in the waterlogged ground, causing the crown of the plant to become more susceptible to rot and the leaves to begin drying along their margins. Pull the mulch back so the soggy soil can dry and reduce watering temporarily. If the plant recovers, prune off the damaged leaves to improve the plant's appearance.
https://www.gardeningknowhow.com/ornamental/foliage/hosta/hosta-plant-diseases.htm