"Print selected rows" option missing in Event Participant listing dropdown actions
This is a core bug introduced during refactoring of task action. I have submitted core PR at https://github.com/civicrm/civicrm-core/pull/12310 . Can you please and if possible comment on PR your test results.

Issue logged at https://lab.civicrm.org/dev/core/issues/185

Thanks

Pradeep