https://www.w3.org/TR/2008/NOTE-WCAG20-TECHS-20081211/G183
G183 implies that links without underlines as part of a paragraph of text can be a thing as long as the color contrast ratio is 3:1 with surrounding text, is 4.5:1 with the background, and changes visually (underline, bold, italics, font size) on hover/focus.
https://www.w3.org/TR/2008/NOTE-WCAG20-TECHS-20081211/G182.html
G182 implies that when color is used to convey information, there should be an additional visual cue separating the text from its surroundings - underline, bold, italics, font-size.
https://www.w3.org/TR/WCAG20-TECHS/F73.html
"While some links may be visually evident from page design and context, such as navigational links, links within text are often visually understood only from their own display attributes. Removing the underline and leaving only the color difference for such links would be a failure because there would be no other visual indication (besides color) that it is a link."