Pleco is not available for Mac but there are a few alternatives that runs on macOS with similar functionality. The best Mac alternative is Syng, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to Pleco and four of them are available for Mac so hopefully you can find a suitable replacement. Other interesting Mac alternatives to Pleco are wenlin (Freemium), Youdao Dictionary (Free) and DimSum (Free).
Wenlin software makes learning Chinese easier and more interesting, for begining students, life-long speakers, and scholars alike. It combines a comprehensive Chinese dictionary, a Unicode text editor, and flashcards. For MS-Windows and Macintosh.
Youdao is a search engine released by Chinese internet leviathan, NetEase in 2007. It is the featured search engine of its parent company's web portal, 163.com, and lets users search for web pages, images, news, music, blogs, Chinese-to-English dictionary entries, and more.