好了，我在这里找到了答案：Running same Jenkins job on multiple agents in parallel in declarative pipeline感谢用户'np2807'。我的代码现在看起来像这样：

def labels=Platforms.toString().split(",").collect{"\'" + it + "\'"}

def generateStage(nodeLabel) {
    return {
        stage("Runs on ${nodeLabel}") {
            node(nodeLabel) {
                stage("Stage 1") {
                   script {
                        echo "Running on ${nodeLabel}"
                        sh 'hostname'
                      }
                 }
            }
        }
    }
}

def parallelStagesMap = labels.collectEntries {
    ["${it}" : generateStage(it)]
}

pipeline {
    agent none
    stages {
        stage('non-parallel stage') {
            steps {
                echo 'This stage will be executed first.'
            }
        }
        stage('parallel stage') {
            steps {
                script {
                    parallel parallelStagesMap
                }
            }
        }       
    }
}

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