I am with both Gizmo's Mom and Valhalla here. What you also have to know is that at one time of my life my name tag had Navigator under the name.
Having paper maps (I still call charts) onboard is essential. When things stop working, all the paper needs to work as intended is that paper, a light source (so you can read it) and a Brain. I do realize that the last is asking a lot of some. If can't work one of those, stick to the blue roads where your cell phone has a good connection.
Like Gizmo's Mon, I am still using one of the old great planners. Mine is a 2015 copy of Street Atlas. It can also be a terrific enroute navigator with no requirement for outside support. All that takes is a GPS puck to make a laptop a tracking GPS with a big screen.
As to planning, I can complete the arrangement of a three week excursion before departure and as the navigator can modify the plan enroute, it is always correct even to the locations for breaks and fuel stops not to mention the location for your EOD - Whatever it is. That can be a Walmart, rest area or a Boondockers Welcome. The planning software is not preferential to anything except what you tell it.
Matt