They are icons, and it was ON by default since i installed cachyos, default settings, i have not even changed icon size, i sent the icons from the “start menu/app launcher” by right clicking an item and then “Add to desktop“, literally nothing extravagant nor weird, just as simple as that.
And what you are doing in your screenshots is “area selecting”, you have to just HOVER over them, don’t INTENTIONALLY try to select them, you will see that the highlight will appear or not depending of several factors… and if the icon is NOT highlighted beforehand it will completely IGNORE the context menu target and will open the default desktop context menu options…
After messing around a little bit more trying to record the bug, i discovered that from top to bottom it’s not always the 3rd item, it’s after every item that has more than one line of text for name… it just happened that every time i tested it the 3rd icon had them… i don’t have many icons to play around yet 
And BTW, changing the alignment of the desktop icons changes the bug direction as well…
So i used the amazing built-in tools for screen capture to show it in a video, idk why i did not do that earlier, that was one of the first things i discovered by accident by trying to open the terminal with “Win+R” after the first boot 
Uploaded to GDrive as video, should be easy to watch: https://drive.google.com/file/d/15s2nnMnCAEgJtybC3D859-ASpGPHhMWy/view
Edit: BTW, in the video when i’m trying to demonstrate the RMB click, i move the mouse around so much because my sensitivity is high and my mouse moves quite alot when i click or try to lift it off the desk, making the SECOND RMB to work as expected sometimes, because after opening the context menu for the FIRST time, any subsequent pointer movement makes the highlighting work again on that icon without getting out and entering from any specific direction or order… so to make it still and consistent i lift the mouse from the desk and RMB while holding it in the air to show that context menu in normal conditions does NOT work as expected…