To fix Internal Exception: java.io.IOException, An existing connection was forcibly closed by the remote host Minecraft error, you need to follow the given solutions.

The Internal Exception Java.IO.IOException error usually occurs when you launch Minecraft, or when the game is underway. This error can be caused by a number of different things.

Enable Java Native Sandbox Enabling the Java Native Sandbox option has helped some users clear up their issues related to io.netty.handler and Java.IO.IOException.