Zotero requires macOS 10.11 (El Capitan) or later, as noted on the system requirements page.

We haven't supported macOS versions before 10.11 (El Capitan) since 2019. macOS 10.11 was released in 2015 and can be installed on Macs released as far back as 2007, including all Macs running 10.9 (Mavericks) or 10.10 (Yosemite). If you're running one of those versions, you'll need to upgrade to continue using Zotero.

You may be able to temporarily run Zotero 6.0.9 on 10.9 or 10.10, but we don't provide any support for old versions, and various features (syncing, site compatibility) may not work properly or may stop working in the future.