Version Krita 4.1.7, Windows 8.1
I can do stroke selection with any colour under the sun apart from pure white (255, 255, 255). You can tell there is an issue because the stroke selection dialog usually remembers the last colour you picked, unless it is pure white. It will happily use and remember 254, 255, 255, but not 255, 255, 255. So for example, pick some colour like red, do a stroke selection. Now do another but pick pure white. You will find (hopefully) that you get another red stroke, not the pure white you selected. It refuses to use pure white or to remember it.

Stroke Selection using pure white works fine under Linux using krita 4.1.7 with Current Brush and Line method and it is remembered between uses. I wonder if this is another Windows specific problem. I'll do a switch and get back ......

Yes, Win 10 and krita 4.1.5 for me behave exactly as you describe. This looks like another bug report.