Regarding the single objects: Luban does not seem to be able to resolve the SVG into individual objects. For getting the letters filled: I’d select Vector mode, and then, when setting up the toolpath, I’d select “Fill” with Movement mode “Line”. That should yield acceptable results.
Lightburn has much more flexibility btw. - if you happen to laser a lot, I’d recommend investing the few bucks.
Tested with a sample font in Inkscape, stored the selection as “Inkscape SVG” and imported it to luban.
Was not filled, but once i changed it to Half Tone, this happened:
As I said: Use Vector, then fill. To illustrate: I created a testfile with Inkscape (which despite(?) being free and open source is a great program!) and loaded it into Luban. It does not look filled in the work area: