Why did the line separator disappear in my Finder window?

Please find attached the picture.
This has happened on all versions of MacOS including the latest.

I had to take a picture of it with my phone, because if I take a screenshot, the line would appear as normal in the screenshot.

This is a software problem because it happened on my previous computer, and when I migrated everything to my new laptop, the problem happened exactly the same way.

Also this problem is not occurring on other user account of the same machine, so it must be some kind of setting that is causing this problem.

How can I solve this issue?