diesieben07

It tells you exactly what the issue is. Just fix it...

Refer to the Optifine downloads page regarding compatibility with Forge.,

Please post the full contents, do not cut off the start. Also show a screenshot of your launcher.

1.16 and earlier do not support Java 16.,

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

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

What version of Minecraft are you using?

The code you quoted is now in GameRenderer#renderLevel and still exists pretty much unchanged except migrated to use the updated render system.

There isn't anything you can do if the mod developers have not fixed this bug yet.

The class transformation is necessary for events to work. So probably not.

Only for modded containers. Have you looked at the interface? It is very simple. Like Luis said, you can just SimpleMenuProvider. Note however that there is no MenuType for the inventory menu and it cannot be opened from the server.

Event classes are class-transformed by Forge to enable a performant event dispatch. IntelliJ probably detects this difference in class structure and tries to hotswap the (unchanged) event class in, which will fail.

Post the installer log.

"Falling Leaves" is a badly programmed client side only mod. remove it from the server and report this bug to the mod author. Side-only mods should simply disable themselves when installed on the "wrong side", not crash the game.

Enable the log window in the launcher and post its contents.