I think the virtual mac screen is limited to 4K resolution, which means you can “zoom” it as much as you want, but you won’t be able to fit “more content” on it. That is to say, there’s a difference between having a huge screen with a
matching huge resolution (which can fit more windows with the same text/content size), and what the Vision Pro is going to emulate, which is more like taking your existing 4K monitor and blowing it up (making each window/text/etc correspondingly bigger, and potentially looking blurry if it’s too big.)
You can probably work around this by adjusting the compositor into a “more space” mode in preferences which makes all the content smaller, but it’s not the same as having arbitrary resolution to match the arbitrary virtual size.
Personally, I don’t want a virtual screen at all, I want all the individual windows on my Mac to hover around me in virtual space (like they do for native visionOS apps), but that’s not supported. It’s a real shame IMO.