> macOS is exactly where people expect native theme

Who are 'people' here? The strawman here is that 'average users' do not expect native theme.

"people" is "most users of the platform". A consistent native platform experience has been one of the cornerstones of macOS since even before OS X came along.

If you ask most people, they probably won't know to identify this as a desirable trait, but what they do know is that if they launch a non-native app it will likely not look or behave according to their expectations. For example, I'm an expert user and even I'm still tripped up by the fact that Slack has a rather anemic menubar, and Discourse's is even worse.

In the native vs not-native look and feel discussion, I hold the opinion that different platforms have different answers. In MacOS, users expect a native look and feel, or at least something close to it.

Windows, Linux and Android users have no such expectations. In fact, in the case of Android, a non-native look and feel could be considered a positive thing since the native android look and feel is kind of terrible.

> or because they have no choice (e.g. with Slack).

Or because they are unaware that there are native apps available, just from third parties. For example: https://volt-app.com/

I heard about that a long time ago, back when it looked kind of dead. Glad to see it's still under development. I'm skeptical though, does it actually support all of Slack's features (or even a majority of them)? The screenshot is rather minimal, showing nothing in the way of unfurls, no formatting beyond a link and an @mention, no userlist, no channel info, no pinned messages, no reactions, etc.