Ich kenne das von ganz alten Dateien die noch aus 1995 stammen und wo jetzt auch keiner mehr weiss was das zugehörige Programm war..........
Nicht von Ordnern......
If the files have no extension, or recognizable Type/Creator codes, the system will treat them as unknown.
That doesn't mean it's actually an executable file, but the Finder doesn't know what it is. In such a case, you need to give the file the proper extension for the type of file that it is.
If you're seeing files and folders replaced by files with a .exe or .lnk extension, those files/folders have been exposed to a Windows PC that is infected with malware. In the case of a flash drive, it has been connected to an infected Windows PC. If you're seeing files on your Mac hard drive showing this behavior, they either got copied or synced from an infected Windows machine, or you have some kind of file sharing that allows an infected Windows PC to access and modify files on your Mac.
In the case of .lnk files, the originals have probably been hidden elsewhere on the disk and are intact. Try showing hidden files and looking for the missing items in a hidden folder on the drive in question. Note that there are normally quite a few hidden folders/files on the main drive with your system, and there are always some hidden items on external drives as well. Do not mess with those if they aren't obviously a repository for the missing files!
If the extension is something like .exe, there's probably no easy solution. Those files/folders may have been encrypted (if the Windows PC was infected with ransomware).