Unbeam Selected Notes ⌃U — Logic Pro keyboard command of the day

  Unbeam Selected Notes    ⌃U

Remove the beam(s) from the selected notes. Makes each note independent.

Control beaming in the Logic Pro Score Editor — Apple Support

By default, a note’s stem direction and length depend on the settings in the Staff Style window. You can change these attributes to improve readability; for example, to group notes meant to be played as a voice in a polyphonic passage.