When I set the setting window.nativeTabs to 'true', it's not possible to use window.titleBarStyle = 'custom'.
I know it works as designed. It says:
Enables macOS Sierra window tabs. Note that changes require a full restart to apply and that native tabs will disable a custom title bar style if configured.
But why it's designed like that? I think it's a loss in user experience. Other editors can have both: custom window title bar and native macOS tabs. Example:
