/usr/share/ucto/ligatures.filter is in uctodata 0.4-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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æ ae Æ AE œ oe Œ OE ij ij IJ IJ fl fl ff ff ffi ffi ffl ffl ſt st ß ss