Serato DJ Pro 2.5.9 is not compatible with macOS Catalina (10.15) or newer because Apple removed 32-bit library support and changed the kernel extension requirements. If you have a Mac with Catalina or Big Sur, you must use Serato 2.6.0 or higher. For Windows, 2.5.9 works up to Windows 10 version 21H2 but is untested on Windows 11.
Would you like the direct link to Serato's legacy downloads page, or a comparison of what’s new in version 3.x vs 2.5.9? Serato Dj Pro 2.5.9 Download