Quick search should disable Jira's default functionality
As Jira's quick search is now showing suggested issues by default it is not possible to use the similar issues functionality any more for the quick search.
If you should keep this functionality, you should disable the built in functionality when selecting similar issues quick search. Now both suggestion menues are shown at the same time which is not good.
You can disable add-on’s quick search from add-on settings. It is disabled by default for new installations. There were no way to disable jira’s quick search, at least I could not find one.