We have this utility function in our Jenkins Shared Library:

static List<String> convertMapToJenkinsEnv(Map<String,String> srcEnv) {
    return srcEnv.collect { "${it.key}=${it.value}"}
}

It seems obvious that this could be an alternative signature and implementation to the current basic built-in function:

withEnv

For us, it's far more ergonomic to work with and compose maps in our Shared Library and scripted pipelines, taking advantage of it's well-defined characteristics surrounding unique keys etc.

It seems as trivial as it could be to implement this.