I mean, take an average person, show them the UI of a current mac, then the UI of windows 95, and ask them which they prefer?

It’s not the only factor, but it is a factor.

To prevent a familiarity bias we should ask them the same question in 1995 with time machined screenshots of current MacOS downsampled to 640x480px.

A border of 1 pixel on a UHD display scalled for a display of 640x480 is 0 pixels.

You can make the same exercise, trying to run for ex Windows in a virtual machine with a 640x480 screen.

Exactly, a current UI would be far from optimal on 30 years old hardware. Furthermore it would look alien, not in a good way, even if Windows 10 would probably feel old fashioned to us in 1995, because of the flat look that was forced when hardware was more limited in the 80s. It's almost a Windows 2 with a few more colors and less borders. Check this site for screenshots https://guidebookgallery.org/screenshots/win203

It would be more sensible to show them a current Windows. Or Windows 7. Or a Mac with visible scroll bars. Or ask them if they would like Windows 11 more with the scroll bar size setting removed.