This is different from vanilla because Minecraft Launcher is not used so Optifine profile in the Launcher will not be created.

Warning: When you download these files and you need to make sure that you get the versions compatible with version 1.12.2. Possibly experiencing more rage than respawning in a lava pool. Thankfully the reality is that once you know how to do it, installation is actually very simple. Most people playing RLCraft on either CurseForge or Technic launchers might feel installing graphic modifications seem difficult due to lack of instructions or information elsewhere. For copyright reasons code from optifine could not be bundled with RLCraft and information about how to install them on CurseForge and Technic launchers has been limited. Many Minecraft users normally will be used to having some graphical enhancements in the form of resource packs and shaders.