Create Marker without rounding ⌃⌥’ – Logic Pro keyboard command of the day

  Create Marker without rounding ⌃⌥'

Creates a new marker at the current position in the timeline. The marker is not adjusted to a bar or quarter-note boundary.

Add markers in Logic Pro – Apple Support

You can add a marker at any position in your project. When you create a marker, it can be rounded to the nearest quarter note, to the nearest bar, or not rounded.