There's an error message for giving incorrect username or password. It's treated as status message by WCAG so needs either role="alert" or aria-live="polite".

I happened to be working on the login page this week and opened PR #7276 including a fix for this issue. 🙂
Craft 3.5.18 is out now with that fix ✨
Most helpful comment
Craft 3.5.18 is out now with that fix ✨