Accessible typography covers body text set at a readable minimum size, generous line height and letter spacing, line lengths short enough to track easily, and fonts that avoid characters easily confused with one another, all of which measurably help readers with low vision, dyslexia, and certain cognitive disabilities, and generally improve readability for everyone else too.
Justified text, all-capital paragraphs, and very thin, low-weight font styles are common typography choices that look stylish but consistently make reading measurably harder for these users, and they show up repeatedly in accessibility usability testing feedback.