So the error is ClassDefNotFound, not ClassNotFound (slightly different). Its looking for a file called CaseInsensitiveMap.class and not finding it.
The class file in question is this one https://commons.apache.org/proper/commons-collections/apidocs/org/apache/commons/collections4/map/CaseInsensitiveMap.html
Sorry just seen it in your zip viewer. So im not 100% sure if this is the reason but I know Forge itself blocks some libraries from running, I believe all apache stuff is part of it. The work around for this is to refactor the apache package to something else, however all dependents must also be modified to suit to the refactor. This means you will need to put all the libs in Intelij as modules and then refactor the imports
Just doubled checked. All packages starting with “org.apache” are ignored. So yeah thats why your getting the error
The simplest way i can think of doing this would be to combine all the libraries together into a single folder and then load the project in Intelij and then refactor the package from there. Intelij will change the dependents as long as they are in the same module (if they are in the same folder then it would be).
If you dont have the source code of the libs then compile all the libs without your code and then run a java decompiler on the output. I would recommend using CRF. There are “Online” decompilers that you can use if you want no download of programs. From there you will have the source code inside a folder so load it into Intelij and refactor