I am having difficulty placing my stl files in the 3d print area in Luban. The background grid hardly shows up in my display (iMac (retina 4K) Big Sur macOS 11.2.3). In fact it only appears when I try to slice an object that doesn’t fit the build platform and trying to load it into the workspace. I fudge it to be within the build space by moving it manually by eyeball/guesstimate using the SM logo that does appear.
I find that adding a model doesn’t usually set the (X,Y) origin to (0,0). I’ve gotten in the habit of selecting the object, moving it to (0,0). Then again after any rotation.