RadioBOSS or Playlist Generator doesn't do it. The problem is somewhere else (e.g. source playlist/folder), not in our software.
Good morning, you're right Dimitry, it doesn't depend on RadioBOSS, I discovered the reason for this error online. I'll post it here, maybe it could be useful to someone else with the same problem: Files starting with ._ are hidden files created by macOS, in particular when the files are copied or transferred to a file system that is not native to macOS, such as FAT32 or NTFS. These hidden files are known as "AppleDouble resource files" and serve to hold metadata information that is not supported by the target file system. Usually, these files are invisible when viewed on a Mac, but they become visible when the disk is connected to a non-macOS system, such as a Windows PC, as in my case. While these files are generally small and harmless, they can be annoying, especially when working with operating systems other than macOS. If necessary, they can be safely removed, but you may lose some macOS-specific metadata information when working with the files on a Mac later. They are not visible by default but you can see them, in newer versions of Windows, such as Windows 10 or 11, there is an option called 'View' at the top of the File Explorer window. Click 'Options' and then choose 'Change folder and search options'.
In the Folder Options window, go to the 'View' tab.
Scroll through the list until you find the 'Show hidden files, folders and drives' option. Select this check box.
Click 'Apply' and then 'OK' to save the changes.
After following these steps, hidden files and folders will be visible in File Explorer. Remember that these files are often hidden for a reason, so be careful not to modify them unless you know what you're doing. Thank you.