Charged-particle $v_3\{2\}$ for event-shape-selected and unbiased events as a function of centrality in Pb--Pb (left) and Xe--Xe (right) collisions. Events are classified according to $q_2$ measured in the V0C detector. Points corresponding to different $q_2$ values are slightly shifted horizontally within each centrality interval for better visibility. Error bars (boxes) indicate statistical (systematic) uncertainties.