The size looks the exact same as this very site to me. It's #5e5e5e (effective, as it's actually a slightly transparent RGBa value) against #fff, so a contrast ratio of 6.48:1, well within WCAG AA standards, and a tiny, slight shift to #595959 would be enough to meet AAA.
You were specifically speaking about serif grey text on white, which is pretty much what I just told you - WCAG AA compliant. [1] You weren't talking about Lighthouse nor mobile specifically, so I just answered with whatever info you gave out.