/usr/lib/grub/i386-pc/fs.lst is in grub-pc-bin 1.99-21ubuntu3.19.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | affs
afs
afs_be
befs
befs_be
btrfs
cpio
ext2
fat
hfs
hfsplus
iso9660
jfs
minix
minix2
nilfs2
ntfs
pxe
reiserfs
sfs
squash4
tar
udf
ufs1
ufs2
xfs
zfs
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