I'm about at my wits end for trying to download a shaders mod.
I have made sure I am using the correct and compatible version of optifine with my 1.12.2 forge (each works separately) but Optifine is NOT showing up in the lower left of the forge mc version, nor is there a shaders option within options-video settings. I have done extract when moving the MOD.jar into the mods folder.
Are you only using Optifine or other mods? If only Optifine, it does not need Forge and I would strongly recommend against it as you'll get much better performance without it (vanilla runs better than Forge with only optimization mods as it is not very well written).
Also, I believe that the "extract" option is only for extracting the files from the Optifine jar, which is just placed in the mods folder if you are using it as a Forge mod\, as the Optifine thread states:
Simple (for OptiFine 1.6.2_C4 and newer)
- Put the OptiFine JAR file in the Forge "mods" folder
- Start Minecraft and Forge should automatically load OptiFine