FAT32 limit on total length of all filenames in a directory combined?

The maximum number of files within a directory of a FAT file system is 65,536 if all files have short filenames (8.3 format). Short filenames are stored in a single 32-byte entry.

That means the maximum size of a direcotry (file) is 65,536 * 32 bytes, i.e. 2,097,152 bytes.

Short filenames in 8.3 format consists of 8 characters plus optional a "." followed by maximum 3 characters. The character set is limited. Short filenames that contain lower case letters are additionally stored in a Long File Name entry.

If the filename is longer (Long File Name), it is spread over multiple 32-byte long entries. Each entry contains 13 characters of the filename. If the length of the filename is not a multiple of 13, the last entry is padded.

Additionally there is one short file name entry for each Long File Name entry.

2 32-byte entries are already taken by the "." and ".." entries in each directory (except root).

1 32-byte entry is taken as end marker?

So the actual maximum number of files in a directory depends on the length of the filenames.