From the download page — the large Download button on the homepage.
If you mean that you're not seeing the Mac download on the download page, you're likely using Safari and some broken ad blocker (e.g., AdBlock) is erroneously hiding the section. Disable it (and ideally switch to a better ad blocker, and/or report it to the developers) or download Zotero using another browser.
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If you mean that you're not seeing the Mac download on the download page, you're likely using Safari and some broken ad blocker (e.g., AdBlock) is erroneously hiding the section. Disable it (and ideally switch to a better ad blocker, and/or report it to the developers) or download Zotero using another browser.