I am using multiple mods on 1.16.4, and the end islands have turned into a rainforest, i don't know why, but if there is something that could fix it, it would be really good, here are some photos i can submit the mods if needed.
bageldotjpg commented
Stop using 1.16.4, make sure you are on latest forge and mod versions for 1.16.5.
This can't be undone unless you have a backup but you can prevent it from continuing to happen