How to set ‘-Xuse-experimental=kotlin.experimental’ in IntelliJ

Are you using Maven or Gradle for your project? I had the same issue with Gradle, but I was able to remove the warnings by putting the -Xuse-experimental=kotlin.Experimental in my build.gradle file, inside a tasks.withType.

For KtorExperimentalLocationsAPI you could try:

tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
    kotlinOptions.freeCompilerArgs += ["-Xuse-experimental=io.ktor.locations.KtorExperimentalLocationsAPI"]
}