Change the column divider lines

Can I turn off the lines between my columns, or keep them on only one side of the schedule?

Yes. Starting with version 2025 you can choose where the interior column divider lines are drawn.

On the Format tab, choose Frame, Highlights | Background Color to open the Frame and Background Options form.
Under Interior Column Divider Lines, choose No Interior Column Dividers, Except on left (dividers only between the columns on the left) or Except on right (dividers only on the right).
Click OK.

A schedule with column divider lines changed