I've been trying to create dashboards and reports to show me what is being added to my sprints in JIRA - the best solution that I've found so far is to use JIRA automation to add a custom comment to the ticket being added to the sprint - so I add a comment like "Added to Sprint X during sprint" - now I can just search for all issues with comment ~ "Added to Sprint X" in there.
Little wrinkle this morning - if your sprint is named like "Q2 - Sprint X" then the '-' will break your search. So using wildcards, change your search to be "Added to Q2*Sprint X" and everything will be great again...