Why should't the default dark mode fulfill basic contrast requirements (in this case WCAG AA is absolutely possible)? It's not difficult to achieve, and the same problem would exist if the website was in "dark mode" by default.
I maintain that no stylesheet can be accessible to everybody. If any accessibility-assessment tool says otherwise, that reflects a failure of that tool to consider some classes of visual impairment.
i can't tell you how much i struggle on a daily basis with websites who have passed these "standards". i don't even have anything serious. i just can't read small text well.
so my browser zoom is 150% by default which i adjust if it's too big. that all i did!
my setting has broken major sites on a daily basis. that tool that another poster linked is broken on my side! that's the tool that's telling people they are not following standards...
so yea, i fully agree with you!