You are correct. There was no OOTB dark mode in 1998. I remember it well because I wasted some time every now and then trying to make one using the appearance control panel. It was frustrating because I could come very close to a universal dark mode. But I remember certain types of text couldn't have their color independently set. One of them (body text? can't remember) used the same color as title bars. Which would make it unusable in a proper dark mode.
I guess I was slightly ahead of my time in wanting system wide dark mode. XP with the theming hacks made me very happy.
Microsoft did actually make a "dark" XP theme. It was available "officially" available but they didn't really market it and it had limited adoption. I stumbled upon it and thought I was v cool for using it.
Another problem with this was that some software was just broken. For some reason, some devs explicitly set the text color of labels in their software to black instead of the system default color, but left everything else—including the background—to use the system's color. So you end up with black on black for your dark theme.
Yeah, I do seem te recall dark mode being better for people with... I think it was cataract? Though with that notable exception dark mode is of course entirely superfluous.
