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
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