I have this css in my child theme css file:

.bbp-topics ul.sticky .bbp-author-avatar {
    display: none !important;
}

But it doesn’t hide the avatar. Any suggestions on how to get this to work properly?

[@robin-w Moderator 5 hours, 43 minutes ago]

This should do it

.bbp-topics .sticky a.bbp-author-link span.bbp-author-avatar {
    display: none !important;
}