I was going to start making my first forge mod, but I keep getting the same error: 

Could not resolve all files for configuration ':runtimeClasspathCopy'.
> Could not find net.minecraftforge:forge:1.16.5-36.2.34_mapped_official_1.16.5.
  Searched in the following locations:
    - file:/C:/Users/Cassian/.gradle/caches/forge_gradle/bundeled_repo/net/minecraftforge/forge/1.16.5-36.2.34_mapped_official_1.16.5/forge-1.16.5-36.2.34_mapped_official_1.16.5.pom
    - file:/C:/Users/Cassian/.gradle/caches/forge_gradle/bundeled_repo/net/minecraftforge/forge/1.16.5-36.2.34_mapped_official_1.16.5/forge-1.16.5-36.2.34_mapped_official_1.16.5.jar
  Required by:
      project :

Possible solution:
 - Declare repository providing the artifact, see the documentation at https://docs.gradle.org/current/userguide/declaring_repositories.html

I am not sure how to fix this. I am using JDK 17 in the path for JAVA_HOME, the forge 1.16.5 (which as a side note I need to switch to 1.12.2, anybody know how to do that?) modding template, have finally given up on asking ChatGPT about this, and would like some help. I have edited nothing in this mod template, and there should be no error. so how do I fix this?

The version you are using is no longer supported on this forum.

Please update to a modern version of Minecraft to receive support.