You won’t ever produce a perfect imitation. UIs based on third-party toolkits are always a pain, stuck in the uncanny valley. They look somewhat like they should, but have all sorts of quirks that break useability: text fields that don’t support standard shortcuts, weird layouts, wrong fonts, buttons that cannot be selected with the keyboard, etc.

It is much, much better to use Apple’s toolkits.

How many shortcuts are there realistically? 50?

That's not the problem, the problem is that I can define a system-wide shortcut from System Preferences and it really is system-wide... unless you don't use the native framework, in which case I'm out of luck.

There are an infinity of little things like this. macOS is powerfully integrated across the platform and you either play ball with it or you don't.

One that's pretty important is accessibility. You're leaving the blind, vision-impaired, and paralyzed users out in the cold, because macOS has a fairly complete system for all those users to make use of the operating system. But it won't work for an app that isn't native.

Probably around that by default, maybe a bit more: https://jblevins.org/log/kbd https://www.howtogeek.com/681662/35-mac-text-editing-keyboar...

But all of them need to work, along with system-wide custom ones.

Text substitution is also an issue.

This is the precise reason I hate web apps with a passion. I want every app on my machine to behave predictably and have a uniform look and feel, not for every UI designer to be able to produce their own unique snowflake without regard for consistency.

This is why many people are frustrated by web applications that do not mimic features they expect from native Cocoa apps.