Maybe it's (type word backwards, then apply cipher)? Unlikely.
f (6) → a (1) y (25) → t (20) l (12) → g (7) m (13) → h (8) → "agth"? no. Try shift 5 forward: fylm sl aswd mtrjm anjlyzy
Given the trouble, the most plausible intended plaintext might be — but that doesn’t match letter counts exactly (film=4, as=2, a=1, word=4, matrix=6, analysis=8) vs your string (4,2,4,5,7). So "mtrjm" (5 letters) could be "word?" w→m (shift -10?), o→t (-10?), etc. Not consistent. Maybe it's (type word backwards, then apply cipher)