Small cancellation groups with and without sigma-compact Morse boundary

We provide examples of classical small-cancellation groups which have non-sigma-compact Morse boundary. These are first known examples of groups with non-sigma-compact Morse boundary. Some small-cancellation groups do have sigma-compact Morse boundary, so this property distinguishes quasi-isometry types of small-cancellation groups. In fact, we give a complete description of when Morse boundaries of $C'(1/6)$--groups have sigma-compact Morse boundary. We also provide examples of $C'(1/6)$--groups where all Morse rays are strongly contracting.