What I observe in the attached image is called anti-aliasing.
This is a way any raster image (and Ai has to rasterize anything when displaying it on a monitor) uses shades of color, applied to pixels, to mimic the gradual incline of a line or a curve. The larger pixels you have (that is a lower display or print resolution), the more visible it becomes. HiDPI or 'Retina' displays have higher resolution (smaller pixels), and these 'staircases' become less visible.

You can read more about anti-aliasing anywhere, including Wikipedia (https://en.wikipedia.org/wiki/Anti-aliasing_filter)

However, it’s true that Ai’s anti-alising algorithms are pretty rough. Shades often clustered too much in banded strips... GPU mode can be especially crude.

Illustrator’s antialiasing was always that harsh and crude, compared to other vector apps, like Xara, for example.
There is nothing really can be done to mitigate it, except for trickery — try to cast the Rasterize effect on the art, with a larger resolution value, and then export the document normally. Or you can just directly export the image larger and then resize and resample it with an external app.
I agree this is not convenient, and I surely vote for this.

There is a problem of jaggered lines in vector shapes in Illustrator. Whenever I am making slant shapes or curves the lines or outlines of the vector shapes gets Pixelated. Please Help Me in Fixing this Issue.

hello, i have the version of Illustrator 24.0 and every shape i dra with the tools are pixelated, as diagonal line, circle, star, every shape that is not completly straight is pixelated. i was talking with the support yesterday for 3 hours and they said its a bug. because its the same on 3 different computers.
i will be very happy to find a solution.

Illustrator's anti-aliasing is very dirty and very-very dark. I personally work mostly on icons in Illustrator and the reason I avoid the application for say simple UI is that the result will be dirty. If I import my illustration from AI to Photoshop or Adobe XD - the whole layout will become much cleaner, lighter on preview and on export from there.

Recently I've encountered a situation when my colleague had a small circle, and for this circle, the stroke's been defined as black and the fill was transparent. In Illustrator it looked like the circle hadn't a hole in its center (because the stroke was wide and the circle itself was small) but in any other application (Ps and even Safari and Sketchapp when exported as .svg) the hole was big and obvious.

See, I can't show Illustrator's export results to my clients, especially on pitches: my layouts will look dirtier than other persons' work. It will look cleaner even if I open illustrator's file in Photoshop and export from there. But it solves the problem on an export stage and not when I'm editing a file. So it's a real problem.

It would be lovely if you implement in Illustrator the same anti-aliasing mechanism as you already have in Adobe XD or After Effects.

Illustrator CC 2018 Lines appear jagged, CPU / GPU shows no difference, simplifying path does not help, and anti-aliasing has been turned off.

Not really a GPU bug since it also happens with GPU turned off. But as you can see on the attachment, whenever I draw a curved path in Illustrator it turns out very pixelated/low Anti Aliasing.