I’m getting the build error

This project currently uses the Kotlin/JS Legacy compiler backend, which has been deprecated and will be removed in a future release.

Please migrate your project to the new IR-based compiler (https://kotl.in/jsir).

Because your build tool will not support the new Kotlin/JS compiler, you will also need to migrate to Gradle.

You can continue to use the deprecated legacy compiler in the current version of the toolchain by providing the compiler option -Xuse-deprecated-legacy-compiler.

The Kotlin compilation is one recipe in a large Make build, and it is not practical to convert it to Gradle

Wait i think that was for JVM. JS is like -Xir-produce-js

If you run with -X it'll tell you all the options

Or create a Gradle project and run with

--debug

to see the arguments passed to the compiler and then copy them