minimal Jenkinsfile to show that when directive does not prevent stage from being executed, only the steps, which means that the agent is still needed

Jenkinsfile

pipeline{
    agent none
    stages{
        stage('linux') {
            when { expression {false} }
            agent { label 'default' }
            steps { echo 'LINUX' }
        }
    }
}

output.log

Console Output

Started by user Admin
[Pipeline] stage
[Pipeline] { (linux)
[Pipeline] node
Running on jenkins-agent-default in /jenkins_agent/workspace/example-pipeline
[Pipeline] {
Stage 'linux' skipped due to when conditional
[Pipeline] }
[Pipeline] // node
[Pipeline] }
[Pipeline] // stage
[Pipeline] End of Pipeline
Finished: SUCCESS