This isn't a really high priority thing, but I assume what is happening here is your leaves dont use the same render system as vanilla, thus with shaders they end up like this? I havent tested with optifine on forge or fabric so it may simply be a bug in iris, if you think that is the case then Ill go pester them instead 👍
thank you for your time!

Yeah, the leaves use translucent rendering at the moment which is probably causing issues with certain shaders. I had a similar issue when testing it with Optifabric earlier. It'll be fixed in the next update :)