Compact Machines version: compactmachines-4.0.0-alpha.6
Forge version: forge-1.16.3-34.1.41
I am not using Optifine: Yes, i am using Optifine.
Link to Crashlog: https://pastebin.com/y9Cdn7BZ
Screenshot (if possible): no?

Description of the problem including expected versus actual behavior:
It was to open Minecraft and enter the game normally.

I open the game and it just closes out of nowhere, during loading.

Steps to reproduce:

1. open the Minecraft 1.16.3 with compactmachines-4.0.0-alpha.6, Optifine and Forge.
2. wait for loading.
3. crash :)

Two things that I'm noticing at first glance.

1. Optifine does like to mess with mods, but I don't think it's at fault here. Just noting that if my next step does not work, try removing it.
2. Judging by the snippet below, you might have a duplicate mod jar in your folder. Can you post a screenshot of the mods directory?

[21:24:23] [main/INFO] [op.OptiFineTransformationService/]: OptiFineTransformationService.initialize
[21:24:25] [main/ERROR] [ne.mi.fm.lo.LanguageLoadingProvider/]: Missing language javafml version [35,) wanted by compactmachines-4.0.0-alpha.6.jar, found 34.1
Exception in thread "main" [21:24:25] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:1052]: java.lang.IllegalStateException: Duplicate key net.minecraftforge.fml.loading.moddiscovery.ModFileInfo@51df223b

Okay. I'm not seeing an obvious duplicate file in there, so I have two other guesses.

1. Optifine is incompatible with your Forge version (just remove the mod for a moment to test that)
2. I accidentally have the mod loader forcing 1.16.4+. I thought Forge was allowing it, but that might be on me.

As an aside, I recommend updating to 1.16.5 anyway, since there's no difference for mods between the two versions. Most mods are already moving to 16.5 since they're compatible anyway.

I feel that you should go for the update. There are some nasty server fixes that Mojang fixed in 16.5, and as far as Forge modders are concerned, it's basically an invisible update. If the modders are lagging behind, give 'em a nudge. All it should take is some metadata updating (on Curseforge) and at worst a recompile of their mods.