I guess that by multiple 'scrums' you mean multiple scrum boards, not projects.
A board is nothing but a view of a filter that allows you to see issues in your backlog, add it to sprints/etc.
If you want the same issues to be in both boards, you can do that by making sure the filters of both boards are the same, or, at least, the issues appear in both.
You can use this documentation.
I hope it was helpful.
Jaime Kirch da Silveira
Atlassian Cloud Support
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