This is an honest worry for an older developer like me. When you're young, your eyes can focus on just about anything. This changes as you get older. A dark mode causes your pupils to open wider, where a light mode gets them to stop down. And if your lenses are imperfect, stopping down helps make things sharper.
I'm posting this as a reminder and plea to younger developers: no matter how much you love your dark modes, please consider those of us who can't focus on them, and give light modes full support too. Thanks!