so when I "configured" my Java project to allow Kotlin, I spent some time reducing the amount of lines of my file (more than 45+ lines of code with expressions and other really cool features),
then I closed my IDE for a quick second, opened it back and then everything reverted back (about an hour progress) with Kotlin not configured.
It was clearly configured when I fully converted my code from Java to Kotlin using the option provided by Intellij IDEA with no issues (yes and then I rewrote it as said above)
There's no more information to provide with, that is if no questions are asked.
I have provided you with the necessary photos and code you would need to have.