Heat map of NICER pulse profiles from GRO J1750-27 as monitored during the 2021 outburst. The black vertical dashed line at spin phase ∼0.95 marks the pulse profile peak for ObsID 01. The bottom horizontal bar shows the color-coded normalized intensity. The color-coded ObsIDs reported on the left y-axis show the bolometric luminosity (as derived by Swift/BAT count rates, see text) at each ObsID as illustrated by the color bar to the right. The vertical yellow dashed line at spin phase ∼0.6 confines the ObsIDs where the secondary peak appears more prominently. Pulse profiles are plotted twice for clarity and bins have been smoothed with a Gaussian filtering for visibility purpose.