Zotero has never supported Z39.50. The whole point of Zotero is that it works in the browser, where modern research happens, rather than using an ancient pre-web protocol.
If your library is in the OpenURL resolver directory, users can select it from the preferences and use the Library Lookup feature to find resources in your library catalog.
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If your library is in the OpenURL resolver directory, users can select it from the preferences and use the Library Lookup feature to find resources in your library catalog.