In the classic projects I often used a project board that contained issues from a few different projects. Would like to be able to apply saved filters to projects boards to do this in the next gen projects as well.
This is not a feature in the next-gen projects yet, and the features implementation is being tracked here:
Make sure to add your vote to help us track interest for prioritization efforts, and you can add yourself as a watcher to get updates on the status of the request.
Also keep an eye on the Next-gen roadmap for Jira Software Cloud as this page highlights the current and upcoming features that are in the works.