It's hard to say just from the look on the results what's wrong. The second image, the screenshot, probably shows how the drawing really is like, with too fat lines. Maybe you have had Draft mode on, which shows only thin lines regardless of how they are really set.
How was the first image made? By Export to Image, as png? This always gives thin lines only. But there are different thicknesses for the circles and the numbers in your image.
Best provide a sample file here. (More v - Upload a file)
I'm not sure about the "draft mode" being on or off. I'm honestly not aware of that setting yet. When I started this drawing I'm pretty sure I set the line thickness to 0.13mm for each layer. I've made other drawings that seem to save and reload without issue.
On the first file, there is not issue !
The size of the dial is 1 mm and the thickness of line is around 0.1 mm so 10% of the global size of drawing. If you change the width of line to 0 mm then the drawing is showed as you intend. Note: this has to be done on the 3 layers used.
As fa201 has already noted, the object is very small. I doubt you really wanted to draw a dial of 1mm diameter, so maybe it's an issue of chosen units. You have units set to None, maybe that's a mistake. Or have you imported elements or the whole drawing from somewhere else? Or accidentally scaled it down?
To fix it, scale the drawing up or set a different unit. You may keep your line weights then.
Also conspicuous, General Scale for dimensions is set at 2.5, which means the drawing is intended to be printed at scale 1/2.5, smaller than true size, with such tiny objects?
In Options - Application Preferences - Defaults you can set the units to be applied to new drawings. You have to close and restart LibreCAD to make it valid. To have also paper size and other settings changed for new drawings you have to make your own empty template drawing with your settings and set that as template in Options - Application Preferences - Paths. Or have it saved anywhere and just open it, you can provide yourself several different versions then.