Beginners Problem with LibreCAD: grid spacing/snap does not seem to work

Boah. I expected that learning any CAD might take some time, but I didn't expect to stumble on my very first draw a line attempt, and not beeing to be able to resolve the issue mysef. I looked at tutorials, I tried to read the manuals, at least the ones which looked promising to help with my problem, but no luck.

I want to draw a floor plan. The room is 8.5m long and 4.1m wide. I want the grid to snap to millimeters (0.001m). I check options - Unit, says Millimeter, OK. I go to options - Appearance and uncheck "Automatically scale grid", then go to Options - Current Drawing preferences - Main Drawing unit and set to Meter, Precision to 0.000 and finally set Grid - X-Spacing and Y-Spacing to 0.001.

Result: zero. If I draw anything, the grid snaps to 100 - 200 - 300. Grid Status says 0.001 / 0.01. I tried several settings for X-Spacing any Y-Spacing, but they seem to change nothing, the snap distance seems always remain the same as stated above.

Where is the problem?

Thnx, Armin.

"Automatically scale grid" in Options - Application Preferences - Appearance only affects the visual appearance of the grid on screen, but not the actual snapping points. So that's irrelevant.
The actual snapping points (if activated by "Snap on grid") are defined by Options - Current Drawing preferences - Grid - X-Spacing and Y-Spacing, in your case both set to 0.001. You have done this right and it works for me. Don't know why it doesn't for you.
But generally it is no good idea to make a drawing based on snapping to grid points, especially if your units are meters and you want 1 mm steps, how many thousands of snap points will there be...
Better learn to work with absolute and relative xy coordinates, switch snap on grid off and let Grid - X-Spacing and Y-Spacing set at Auto.
What LibreCAD version do you use and what is the intended printing scale?