This looks very similar to this issue: Admin: Journal-Settings: 'Sections' tab loads over 60 seconds! - #13 by Commifreak, where the problem is also with the same JS request. There is an intermediate solution described by adding pagination to the page (below the linked comment).
I see also that the issue is already opened here: Issue grid slow on journals with very large issue lists · Issue #7051 · pkp/pkp-lib · GitHub