Sounds a bit pedantic, but this was the reason I could just not use macOS as a daily driver. IIRC, there was a brief period of time where this anti-feature could be disabled by some obscure command, and the switch was instantly. But this was later gone in an update, which ultimately taught me the lesson that one should not be at the complete mercy of some OS updates.

Is there any way to change the delay for that? I would think that tucked away somewhere under the hood there’s a setting that controls the animation duration.

Being able to turn that down or off would be a boon to my productivity.

I must be missing something because my Mac OS does not do that. There is a slide-in/over animation, but it's nearly instant.

"Nearly instant" is a massive loss of usability compared to "instant". The quicker the transition the less disruption there is to your short term memory. If it's instant then switching between virtual desktops is almost as good as having multiple monitors. If I have to wait for even a brief animation (and MacOS's animation is painfully slow) I'm likely to forget details, which means I'll have to switch again, and risk forgetting even more.

You can change the default slide-in/over animation to a faster fade-out/fade-in one by enabling "Apple menu -> System Settings -> Accessibility -> Display -> Reduce Motion", but you cannot disable the animation completely.

My guess is that there’s a Reduce Motion option in the accessibility preferences like on iOS.