The “show user menu avatars” setting seems to affect more colors and styles than expected. Note the bold style on the username and the color of the links. Top image is with “show user menu avatars” enabled, bottom image it is disabled.
Additionally, this seems to cause weird effects when leaving a hover state on a dark color scheme, for instance when the right mouse button is pressed and the notification is opened in a different tab.
Perhaps we can improve the visuals of this state… but this is the focus state of the link which, for accessibility purposes, is expected to remain when opening a link in a new tab.