When new chunks are loaded in vanilla minecraft they simply "appear instantly", with this mod they can be animated to either appear from below or above. This mod shouldn't impact fps considerably because all it does is render chunks "somewhere else".
Once you install this mod it will be in mode 0, that means that all chunks will appear from below. In the config file you can switch between 5 modes and also change the duration of the animation. In addition you can also enable an option that makes chunks that are close to the player not animate
You can also change the easing function that is used in the animation, this is a website where you can compare them.
On versions below 1.13.2, this mod supports forges config menu so you can switch between modes,easing function etc. ingame.
To learn more about how the animations can be configured, visit this page on the config.
OptiFine is supported, however on 1.14.4 and above for the chunks to be animated you will need to make sure the “render regions” option is disabled. This can be found under the Performance screen in Video Settings.
Feel free to add this mod to your modpack