Forge version: 14.23.5.2854
Twilight Forest version: <twilightforest-1.12.2-3.11.1021-universal>
Link to crash log: crash-2021-01-08_02.30.54-client (i'm new to this so i'm not too sure if im doing it right?)
crash-2021-01-08_02.30.54-client.txt

Steps to reproduce:

1. Install Hexxit Updated mod via CurseForge (from Twitch)
2. Install <OptiFine 1.12.1 HD U C7>
3. In File Explorer: My PC>Documents>Twitch>Minecraft>Instances>Hexxit Updated>mods
   Move <OptiFine 1.12.1 HD U C7> to "mods"
4. Go back to CurseForge
5. Click "Play" at Hexxit Updated
6. Minecraft Launcher page
7. Minecraft version shows:
   Hexxit Updated
   forge-14.23.5.2854
   
8. Click "Play" within the Minecraft Launcher page
9. Minecraft starts to load, initialising
10. Minecraft crashes before loading or starting up the game.
    
11. End.

What I expected to happen:
To be able to launch and play Minecraft

What happened instead:
Initialisation error after attempt to launch Hexxit Updated mod on Minecraft

This issue has been solved! Optifine was the issue. Apparently it clashes with some of the mods within the folder when launching Minecraft.
To solve:

1. Remove Optifine file from "mods" folder.

Other possible issues/solutions:

• Error to certain actions within CurseForge -> Check to see if you are signed-in to CurseForge
• (Within Minecraft when joining someone else's server) Connection lost /n Server Mod Rejections: /n <>: Requires version XXXX but mod is not found on client. -> Go to CurseForge and the mod you're using. Search for the mod that is in and click on it, it should direct you to the author/owner of the mod. Search for the version of the mod that is shown in the Minecraft error page. Download and drop it into the folder. Delete the original version of the mod.

Hope it helps someone else who might've needed it!