How can I just show the preview panel without the note edit panel?

You can do that by turning off that the note edit panel is the central widget in the Panel settings.

Then best create a new workspace Preview only by clicking Window / Workspace / Add new workspace in the main menu. You will be able to switch between different panel layouts.

Afterward you can turn off the note edit panel in the Window / Panels menu.

Keep in mind that you can move around all panels as you like by clicking Window / Unlock panels in the main menu. You can also resize all panels to fit your needs.

Alternatively you can switch to the Preview only layout in the Layout settings.