There is no extra setting to improve the printing of default-width lines. The default width is 0.00mm.
You have to take care of setting a proper line width when drawing, or change it afterwards via properties, or attributes, or layer attributes. Out of the box the line width is "By Layer", and in the layer attributes it is 0.00 mm.
This constantly produces troubles for newbies. Some while ago I already have suggested to change the default width to practical 0.25mm out of the box, but there seems to be some hesitation to do so, probably to stay with AutoCAD conventions. But I don't have access to AutoCAD, so I don't really know how they do it.
I started looking for a way to select by attribute. Is there a way to select all lines with a width of 0.0mm?
I didn't want to select all (by dragging around the whole drawing), because I had already changed some lines to a custom width.
I tried searching for that concept in the new manual, but of course I don't know the terminology, so I don't know what to search for.
Also, where do I set the default line width in the default layer for future drawings? I don't see that under Options / Application Preferences
( I did find and set dimension width under Current Drawing Preferences, and I found the Layer Attributes which set it for this drawing. )
There is no selective filter option. More advanced commercial cad programs do have this, I know. Maybe in a couple of years...
If you have already changed the width of some lines, you can select those with the mouse, then do a "Invert Selection" and use "Attributes" to convert only the rest.
You can't set the default line width for the entire application. But you can set up and save an empty drawing with your settings and use this as a template for future drawings.
You can even set this for automatic start up for a new drawing in Application Preferences - Path - Template.