eggplant

Answer 1

This is likely Rust fungus.
Neem Oil can be used to treat the fungus.
Make sure you are watering at the soil level, not splashing water on the plants themselves.
Good air circulation is helpful in control of the Rust fungus.
Here are some articles that have more information.
https://www.gardeningknowhow.com/plant-problems/disease/learn-about-plant-rust-disease-and-rust-treatment.htm
https://www.gardeningknowhow.com/edible/vegetables/eggplant/eggplants-turning-yellow.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm