That's not true. UIs became light when CRT monitors became capable enough to display bright light colors, which people preferred due to resembling printed paper

That's not true. UIs became light when CRT monitors became capable enough to display bright light colors, which people preferred due to resembling printed paper. Before that it was all white/gray/green text on black/dark blue backgrounds. E.g., DOS vs Windows. And people were adding filters to their CRT screens due to fearing brightness and radiation. Ofc, it was the flicker that actually made people's eyes tired, but filters have been common at least since the 90s, and mostly snake oil. Today's screens aren't insanely bright at all, due to auto-brightness setting, with devices able to detect the ambient lighting and adjust. You can also control the color temperature depending on tone of day, which became a standard feature. It's not 100% perfect, but has been working well for me with iOS, Android or macOS devices.