Exhibit A: the unfathomably unreadable new look in macOS 11.x. It was already bad in 10.x but they made it worse.
Exhibit B: This is what happens when you go to System Preferences / Accessibility and check "Increase contrast". It just puts thin black borders around everything.
Exhibit C: This is what happens when you move the "Display contrast" slider two ticks up from "Normal" to "Maximum". It makes it so much worse that I wonder if someone implemented the slider backwards and QA didn't notice.
"Dark mode" is just as bad, it all ends up being dark gray on dark gray instead.