DaemonUmbra

You have duplicates of Waila/Hwyla/Jade (They are all forks of the same mod)

So you're putting your mods in C:\Users\blake\AppData\Roaming\.minecraft\mods?

Are you able to access https://launchermeta.mojang.com/mc/game/version_manifest.json in your browser?

Please use one of the paste sites in my signature below instead of MediaFire

Multicraft needs to update their manifests to run a script instead of a jar, or do more than just run a file

The fix I usually recommend is deleting the folder those are in and the vanilla jar they are derived from (1.16.4.jar in this case)

Did you use RagnamodVI's server pack or did you take the client and dump it onto the server?

Note that this only works when the config is the issue and you should check the log first

Unfortunately you might need to completely reinstall Java, the error you're getting should be impossible

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

The GAME log, which might have things missing if the game crashes too early

Forge should not be modifying existing installations except the one it initially creates, have you been using this one instead of making a custom one?

You accidentally installed the fabric version of hwyla and it's pulled in the Fabric API

Please provide debug.log (more info on where to find it and how to provide it can be found in my signature below, just expand the spoiler)

Have you tried disabling Avira while the installer runs?

Did you retry the installation? How good is your internet connection? What antivirus do you have?

Optifine is notoriously invasive and just as notoriously closed-source. If Optifine doesn't work properly when combined with Forge it is their issue to sort out as they can see exactly what happens inside Forge but we cannot do the same with Optifine.

What happens if you try manually running the installer?

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Something is looking for CuriosAPI and not finding it

Try removing Optifine as a first step

That depends on the search provider and their web crawlers

Where did you get the installer from and did you do anything to it?

Are you both also using Strato V and both also getting this spam?

It was already decided that the rule of thumb is LTS will be the version immediately preceding the latest (excluding transitionary versions which will be skipped for LTS qualification)