DaemonUmbra

Please provide the installer log (more info in my signature below)

Optifine issue, not on Forge to fix

If you're going to provide a log please provide the full log

terraheads is a component of terraqueous, apparently

Please keep this forum in English. Please provide your installer log (more info in my signature below)

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

Those images are completely broken, please provide logs as described in the "Logs" section of my signature below

Not just Optifine, it's also looking like terraheads is trying to register an ItemStackRenderer on the server

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

Please don't necro old threads. If you have an issue make your own thread.

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

Don't use com.willatendo unless you own willatendo.com (Check out GitHub Pages for a free website) It would be easier to test things if you posted your code as a GitHub repo.

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

Is the issue launching the game or installing Forge? Either way, please provide logs. (more info in my signature below)

I recommend CurseForge. The site you mentioned is almost certainly a repost site. Check out Stop Mod Reposts for more info. Edit: Forgot to answer your actual question, correct 1.12.2 mods will not work on 1.16.1.

Hooray, someone who figured it out on their own

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

Forge and other Minecraft mods do not work on versions other than the one they were designed for, so yes you need to use versions that are specific to your version of Minecraft

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

If your bat has “pause” at the end... yes that’s what happens. What you need to do is instead of pressing a key, copy everything that the server printed, post it to one of the paste sites in the “Logs” section of my signature, and link it here

It sounds like you're running a Forge client on a Vanilla server, how are you starting the server?

We don't give a definitive level because too many people will race to it and ignore all else, and learning by modding tends to lead to people picking up bad habits. I can tell you your issue is a lack of understanding the difference between resources and code.

Don't learn Java by modding, learn Java BEFORE modding

Do you know Java or are you trying to learn Java by modding?

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