Hey, sorry for bothering. I just watched this video where the woman just used gradle to build a project or something. Tried the same but on Windows and after one minute or so it said:
"Deprecated Gradle features were used in this build, making it incompatible with Gradle 5.0."
I would try importing Forge in Eclipse or IntelliJ (I like Eclipse more tho) but I have no idea how I would do that since I've never worked with Gradle in the first place.
Edit: Just found out in a random GitHub issue that "setupDecompWorkspace" is not used any more. It's "gradlew eclipse" now.