Google's Jpegli encoder can encode with 10+ bit precision which could theoretically alleviate the issue just as 10 bit helps with video, though I haven't tried the associated decoder yet. When decoding with a typical 8 bit JPEG decoder like that bundled in Chrome, the artifact still occurs.

Ok I gave it a try, there's still artifacting under djpeg (and then I noticed sRGB images still have visible artifacting but less) but it does seem to smooth out the "mosquito noise" more. Interesting. Maybe I have to feed the encoder a 10bit sample.