Can flip this around: lots of websites now default to dark mode because reasons, and dark mode is very difficult for me to read (all blurry, also gives me a headache after a while).

Yes, the correct way to approach this is to make good versions of both and respect the user’s preference. Font size is similar: you’ll never make everyone happy with a single choice so you should respect the user’s ability to know what they need.

I think both dark and light modes are an accessibility option.