Shaders and resource packs are the way to go, but if you don’t know how to add them to your game, we recommend checking out the following links to get started.
CurseForge is our preferred source and what we’re familiar with, but you can find alternatives if you’d like. Just make sure anything you find matches the server’s game version of 1.19!
Note: The server is Fabric and utilizes the Iris Shaders mod, which means you don’t need Optifine installed.