On infinity a long press will collapse all comments replying to that comment.
With the "Fully collapse comment" setting enabled (under Interface->comment) it will collapse that comment too.
The setting "Swap tap and long press in comments" (under Gestures & buttons) will make it so tapping has that effect instead.
In the comment toolbar, to the left of the save comment button there is an up arrow that also triggers the collapse of the comment.
On infinity a long press will collapse all comments replying to that comment. With the "Fully collapse comment" setting enabled (under Interface->comment) it will collapse that comment too. The setting "Swap tap and long press in comments" (under Gestures & buttons) will make it so tapping has that effect instead. In the comment toolbar, to the left of the save comment button there is an up arrow that also triggers the collapse of the comment.