Fg-optional-4k-videos-3.bin

Open the file properties. A 4K video, even compressed, is rarely small:

If fg-optional-4K-videos-3.bin is only a few megabytes, it’s likely a file header or index chunk, not the video itself. If it’s several hundred megabytes to gigabytes, it contains substantial data. fg-optional-4K-videos-3.bin

This simply indicates that this is the third volume of the 4K video pack. There is likely a fg-optional-4K-videos-1.bin and fg-optional-4K-videos-2.bin somewhere else in your download folder. Open the file properties

To avoid finding yourself questioning mysterious .bin files again, adopt these practices: If fg-optional-4K-videos-3

This tells you exactly what is inside the compressed archive: video files in 4K resolution. Modern games often have pre-rendered cutscenes (cinematics). Developers include multiple versions of these videos: one for 1080p screens, one for 1440p, and one for 4K. If you don't have a 4K monitor, these files are a waste of hard drive space.

The trailing -3 indicates this is likely part of a sequence. There may exist fg-optional-4K-videos-1.bin, ...-2.bin, and so on. This strongly suggests a multi-part archive or a segmented download.