We have updated the Splunk Enterprise version to 9 recently. Regarding post upgrade validation, I have already gone through this - post
In addition to these validation steps, I need to ensure all the dashboards, search reports/alerts, lookup files are working as expected in each app.
If this can be achieved via manual check of each dashboard/report, then it will be a long process. There are so many dashboards/reports available in each app.
Could anyone please let me know if there is a way to ensure the working of all splunk objects post upgrade?
There is no Easy Button for that. Presumably, each dashboard, report, alert, etc was tested when it was created. Repeat those tests to confirm the objects are working post-upgrade.