To change Gallery Strips to 2 columns on Desktop, 1 column on Mobile, you can do these.
#1. Hover on top right of Gallery Strips> Click Edit Section
#2 . You can adjust the Row Height. With each Row Height value, Gallery Strips will display a different number of columns of images.
With this option, Gallery Strips will show as 2 columns on Desktop and always show as 1 column on Mobile
