So, long-story short, I was playing on an MC server with friends, when I noticed something was off with my texture pack, which made leaves more bushier, but wasn't compatible with fast graphics. Same thing happened with water, it showed the solid-looking fast water instead of the translucent one that should show up with fancy graphics, what's the issue?

Same with Iris, non-translucent water with Fancy graphics and shaders disabled.
Finding clay was impossible so I installed an Iris shader. It didn't even occur to me that the water is translucent in vanilla, I've been an absolute zombie lately.

I don't think it's an Iris problem, I uninstalled Iris to see if it changed anything and the water wasn't translucent.