A similar report, but with a long stroked line with a variable width:
http://illustrator.uservoice.com/forums/601447/suggestions/50688200

Yes, I can confirm. I attach the test file.
Illustrator’s GPU preview has a lot of problems with thin objects... especially apparent when the stroke weight is zero, http://illustrator.uservoice.com/forums/601447/suggestions/46443136

Now i noticed, that if i want to make a form with the two outer circles it comes again

I’ve noticed that when I draw a circle with a diameter of 250 mm and a stroke thickness of 0.25 pt, with the stroke alignment set to inside, and then draw another circle with the same stroke thickness but a diameter of 230 mm, the smaller circle shows irregularities in the stroke line (see images).

When the stroke alignment is set to center, however, the circle is displayed correctly.
This issue isn’t serious, I just noticed it while working.

0.01的圆形线条和0.02的圆形线条非常粗糙

OS MacOS Ventura 13.2.1
M1 Pro Macbook Pro

Please see attached illustrator file

There is an issue when applying a stroke on curved lines in Illustrator 27.3.1

This is visible with strokes of 3pt and under. As the stroke decreases in thickness, the graphical error become more dramatic.

Still, it is a bug, so thanks for reporting it!

The problem is about duplicate objects on top with black strokes with 0 weight. Why do you have these in the first place?
GPU can’t handle these well, and it’s a known bug, similar to this one: https://illustrator.uservoice.com/forums/601447-illustrator-desktop-bugs/suggestions/43532958-jagged-artefacts-on-edges-of-objects-with-gradient
Try either of these:
— Remove duplicate objects
— Remove black stroke from these objects
— Increase the weight
— You can also switch to CPU mode, but it will just hide the problem

no funciona bien

No funciona bien el trazo

I've been experiencing this same behavior on my new 2021 MBP 14" (M1 Pro) with the latest OS (Monterrey 12.1). A lot of my artwork has "junk" along curved lines. As Egor mentioned, this only happens when GPU acceleration is enabled; disabling it seems to 'fix' the problem. See the attached screenshots.

I didn't notice this on my Intel MBP, but I didn't use it much and mostly used Windows PCs before this; I never noticed this problem on Windows.

Philip, it's one of many existing GPU rendering bugs Ai has.
Can you make a copy of your file, remove everything that does not influence the bug, and share it here?

Mac OS Monterey 12.0.1
Illustrator 26.0.1

I have been drawing lines with the line tool and expanding and bending them using the Anchor Point Tool. Sometimes Illustrator creates a secondary line alongside my smooth one that is jagged. It is still visible if I zoom in or out but I don't think it's really there (as a vector path). It is visible in the middle of my screenshot.

This is a GPU rendering issue.
A workaround is to disable it temporarily.

Craig, this is a common GPU rendering problem :(
I can confirm this also happens on my machine.
The workaround would be to switch to CPU mode in cases like this. Hopefully it will get fixed eventually.

Stroke does not display correctly for very fine stroke lines on curves (for example 0.001mm). If the change the stroke to 0.1mm it displays perfectly, but when 0.001mm the appears to be large vectors filled in. There are not "really" there - it is just a display issue, but very easy to reproduce.
Since 0.001mm is a common stroke width for Laser Cutters, this is a big problem as it is difficult to work with detailed drawings when it does not display correctly. See the attached sample for a very simple example.

Adding points mitigates this issue, but doesn't solve the cause. I'd rather not have to add points to work around a software issue. This particular issue only manifests when GPU Preview is enabled, and does not seem to have any effect on CPU rendering.

the outline stroke of text is not smooth when set the stroke weight to 0.1mm

Try this - go to stroke, change CAPS and CORNERS to round (middle buttons).