The current limitation in Jira Cloud is 5,000 per https://jira.atlassian.com/browse/JSWCLOUD-20432. However, we quickly run into this limit when we try to adapt Advanced Roadmaps for Program and Portfolio-level views. We  use these broader views to aggregate data across all of our squads to shape the strategy, align the underlying work, and track progress as we go.

We are a relatively small shop and already running into the 5,000 issue limit, so I'd imagine larger enterprises have this issue too. Please let me know if anything I can add or clarify.