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That’s running on Java 17; are you somewhere setting a toolchain or otherwise using Java 21?

I have a android module that can't run on java 21 yet that i exclude it in the root build.gradle.kts:

tasks.withType<KotlinCompile> {
    kotlinOptions {
        freeCompilerArgs = listOf("-Xjsr305=strict")
        jvmTarget = if(project.name == "android") "17" else libs.versions.jvm.target.get()
    }
}

in the backend build file, i've set :

java.sourceCompatibility = JavaVersion.VERSION_21

with kotlin jvm plugin 1.9.21

Sure, but the underlying jvm is 17 therefore incapable of source=21. Run on Java 21 or (better) use toolchains.

thanks for educating, i used toolchains in each module and removed jvmTarget alongside source compatibility( since toolchains infer it)