No, there's no "merge" function, but it's really not hard to copy one filter, add an "or" to the end of the other one and paste the first one into it.
Or, some add-ons give you a JQL function for "issue in filter (<name other filter>)"
I don't know what you mean by "cross in backlog view"
They ask you to raise an enhancement request at https://support.atlassian.com/contact
But if you do, you'll find it closed as a duplicate. You would be better off voting on the existing ones in https://jira.atlassian.com - I'd expect to find them in the search https://jira.atlassian.com/issues/?jql=project%20%3D%20%22JIRA%20Software%20Server%20(including%20JIRA%20Agile)%22%20and%20text%20~%20%22quick%20filter%22%20and%20text%20~%20merge
I have multiple projects that use variations of the same base workflow. The variations depend on the requirements of the project or issue type. The variations mostly come in the form of new statuses ...
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