Will be fixed in Plasma 6.2

https://pointieststick.com/2024/06/28/this-week-in-kde-everything-i-think/

Are you using the default Breeze theme?

I’ve heard such issues can arise with 3rd party themes, so I just stick to Breeze. I’m using Breeze Dark and I have not seen this issue on Plasma 6.1.

Try deleting or renaming ~/.cache/icon-cache.kcache

Can not reproduce with stock Breeze theme on Arch

I’m also experiencing this bug, regardless on which theme I set (Breeze, Breeze Dark, Breeze Dark EndeavourOS, Breeze Twilight). The folder icon is the only one with this problem, and only when the window has focus