Toxic Sky & Plastic Seas
Toxic Sky & Plastic Seas is a Minecraft modification created specifically for Modfest 1.20 "Sky and Sea".
The mod transforms regular rain into green acid that damages items equipped on the character or dropped into the world. In deep ocean biomes, plastic garbage patches appear that can be collected and recycled into plastic armor immune to acid precipitation.
You can disable acid rain using the convertRainToAcidRain game rule or configure which items and entities should not take damage using the #toxsky:immune_to_acid_rain tags for items and creatures.