Playne is now available for Mac OS via the Apple App Store and itch.io. Playne for Mac won't be released on Steam since Steam doesn't support platform based reviews.  If you purchased Playne on Steam you can still receive the Mac version for free via itch.io by sharing your profile ID showing your Playne purchse.

Playne (MacOS) : https://apps.apple.com/gb/app/playne/id1518592721

Please also ensure that your Mac meets the minimum requirements as follows:

Minimum Requirement:

OS: 10.13.6 (High Sierra) or later

Processor: 2.4 GHz Intel Core i3

Memory: 4 GB RAM

Graphics: Nvidia or ATi GPU with 2GB Memory

Storage: 4 GB available space

Recommended:

OS: 10.13.6 (High Sierra) or later

Processor: Intel i7

Memory: 4 GB RAM

Graphics: Nvidia or ATi GPU with 4GB Memory

Storage: 4 GB available space