https://github.com/QualityOps/wdio-timeline-reporter#readme
Step 1: Add wdio-timeline-reporter in dev dependency "wdio-timeline-reporter": "^5.1.1"
npm i wdio-timeline-reporter --save-dev
Step 2: Add timeline in services of the wdio config file
Step 3: Add timeline in the reporters for wdio config along with output directory for report.
Step 4: Run your tests and you will report generated in output directory.