Joke aside, looks like your screen brightness is too high to begin with. If it's set correctly, a light mode tab in an otherwise dark UI should be a mild disruption, not something that blinds you.
Legitimate suggestion: get into the habit of controlling the screen brightness and your eyes will thank you. There are DDC utils that let you control the hardware brightness (and other parameters too) of the monitor via software. I for example like ClickMonitorDDC (works well even if it's practically abandonware), you can do things like scheduling based on time of day and controlling multiple monitors simultaneously.
I'm over 70 years old and I know exactly what hurt my eyes. White background with dark letters are fine in a book, but white in a screen is because it is a light with all pixels on. There are no much contrast with dark letters apart it dazzled my eyes. White letters on a dark background are much more confortable and readable for me, yes or yes.
Fair enough. I'm not saying "don't use dark mode", I'm saying don't rely solely on it. Dark mode with brightness cranked up to 100% might be worse than light mode at 20% brightness if that's appropriate for the ambient light you're in.
I agree about contrast; to me white text on black background is about equally as bad as black text on white background (but fortunately most dark themes are not white on black). I look at text all day long and usually prefer something with a medium gray-ish background and light letters; in very rare cases I'd resort to a light theme just for its contrast (e.g. working on a laptop outside during the day and I can't bring the brightness any higher).
For my old eyes a 20% Brighness is even worse for me to read the content without putting my nose direct on the screen. But yes, dependig on the contrast settings, also white letters on black background can be dazzling, but no t so in a normal contrast, at least for me.
I wish it were better integrated into GNOME / KDE so I could simply use the brightness controls on my keyboard.
I set my brightness to maximum because I work next to a window, but it's the power of a million suns at night, especially on a high-end, colour-accurate monitor
In my experience it's pretty well integrated in both GNOME nad KDE
I had to work to work with a plethora of keyboards on both and they always worked if I remember right