I'd estimate I've probably spent 100+ hours testing and fixing dark mode issues over the past 5-10 years. Investing "a little bit of effort" is how I got myself into the trap of doubling+ UI QA time to make sure everything _also_ looks good in dark mode (and also in dark mode across a matrix of other configurations) every time I want to ship anything new to users.

I know some people care about dark mode (and that's why I bit the bullet to add it), but I'd honestly much rather have spent all that time working on actual features.