the 'txt" extension outside WinSCP has an icon associated to NotePad++ and i checked the registry under Computer\HKEY_CLASSES_ROOT\Notepad++_file\DefaultIcon to see it was already assigned the correct icon. So it seems it is a some kind of bug with WinSCP not windows.
not a big deal but for years seeing it blank has been annoying.
For the life of me, over the years and version and across different fresh installs of WinSCP i have never seen an icon associated with .txt files despite being associated with NotePad++ .. I do notice WinSCP does not like to give icons for apps taht are located in the \Program Files dir vs the Program Files (x86) but that is another story....
See attachment. I am using the standalone WinSCP (didnt use an installer).