Distributing a Python desktop app on Windows and Mac — the full release pipeline

WP Maintenance Manager ships from a single Python codebase to both Windows and macOS. "Python is cross-platform — write once, run anywhere," the saying goes. The reality is that the distribution pipeline is completely separate per OS , each with its own pitfalls. PyInstaller / Inno Setup / Apple Notarization / eSigner — the release cycle is a combination of OS-specific toolchains. Here's the full picture, plus what to watch out for at each step. (The choice of internal architecture, Flask + browser UI, is covered separately in why we built a desktop app on local Flask + browser UI ; this post is about distributing that architecture across two operating systems.) The per-OS pipeline at a glance Step Mac Windows Build PyInstaller ( --target-arch x86_64 ) PyInstaller Distribution format .app bundle → .dmg folder → .exe installer Installer creation hdiutil / create_dmg.sh Inno Setup ( .iss script) Code signing codesign + Developer ID certificate eSigner CSC (cloud signing) Pre-distribution validation Apple Notarization SmartScreen reputation buildup Final artifact WP_Maintenance_Pro_X.X.X.dmg WP_Maintenance_Pro_Setup_X.X.X.exe Both OSes share PyInstaller, but the path diverges from there. Mac sits inside Apple's review process; Windows runs through Microsoft's reputation system. They're fundamentally different ecosystems. Mac — PyInstaller → sign → Notarization → DMG The Intel / Apple Silicon trap The first trap in Mac PyInstaller builds is architecture . Running pip install + python build_app.py on an Apple Silicon Mac without thinking produces native binaries (like cffi ) for arm64 only — which then don't run on Intel Macs at all. The fix is to run the entire build through arch -x86_64 : arch -x86_64 pip3 install -r requirements.txt arch -x86_64 python3 build_app.py That produces an .app containing only x86_64 binaries, which runs natively on Intel Macs and through Rosetta 2 on Apple Silicon — a unified distribution. Sign inside-out The .app PyInstaller produces conta