Great question! It doesn't add commas to an auction's bid history or placeholder bid text, as marked with stars in the images below. It also does not show commas in the pre-purchase confirmation modal from shops or the "+[x]Potatoes" addition on some Trade Lots.
The Tampermonkey version can be used with Tampermonkey on Firefox and Chromium-based browsers. The Violentmonkey version can be used with Violentmonkey or Greasemonkey on Firefox and Chromium-based browsers. I don't know why one version won't work for both ok it was hard enough learning about arrays