for what it's worth, my ophthalmologist recommended I use light mode only, with reduced blue and red (because red light actually activates the blue cones too apparently)

Then my screen time started affecting my sleep so I still use dark mode at night

But anyways all software should be configurable and follow the parent software (browser, OS) by default, css even allows for that now. There is even a "prefers-contrast" property in order to design for people who need high contrast stuff.