This is what "wagonik4b_sb" looks like in TG.
@N-drju: I loaded your file into Blender 2.92, selected all parts in Layout mode
and then under "Object" I clicked "Shade Smooth". But I do not even know if that had any effect on your model.
Also - since I do not know anything of Blender - I do not know if that has any effect on the model or just the viewport representation.
Anyway, in your very first screenshot I can see that you have Xray mode turned on in the viewport.
Maybe that has something to do with how the model is displayed? Your last screenshot does not give (me) any clues whatsoever.
But as you can see, sboerners object model is the way to go.
It is not a software nor hardware problem, it`s your modeling technique.
CHeers, Klaus