In vertical scrolling using less the page up and page down keys are working. Which keys scrolls one page down/up vertically? The less was started with -S option.
page up and page down alternative for horizontal scrolling in less
linux;terminal;less
From man less:-# or --shiftSpecifies the default number of positions to scroll horizontally in the RIGHTARROW and LEFTARROW commands.  If  the number specified is zero, it sets the default number of positions to one half of the screen width.  Alternately, the number may be specified as a fraction of the width of the screen, starting with a decimal point:  .5  is half of the screen width, .3 is three tenths of the screen width, and so on.So you may run less -S -#.9999 if you want to scroll almost a full page left or right, by hitting left or right arrow key (Esc-( and Esc-) should work as well)