Those aren't lines, they are edges. "They" aren't drawings either, but 3D models or models for short.
The "jagged" lines aren't jagged, they are just not ( or not fully) anti aliased.
If you select the screen settings in the small menu bar on the bottom-center of the Fusion 360 viewport, select "Effects", you can enable "Antialiasing". If it is enabled, we'll have to look into this further.
In that case you might just have to live with it š
Just to be clear, there's nothing wrong with your model or your computer!
Antialiasing is simply a visual effect that sometimes works better than others. You will see a lot less of that if you choose the "Grey room" environment, for example.
That a bummer. I wonder why my Mac does it? I was watching tutorials and the was using a Mac that didnāt do it.
just posting this in case anyone needs it. on top right you can find this
uncheck the "Limit effects to optimize performance" box and you'll get the better display.
then you can select anti aliasing at the bottom middle of the screen.
Hope it helps!