Let’s assume simple ROT-5 on "fyltr": f(6) -5 = a(1) y(25) -5 = t(20) l(12) -5 = g(7) t(20) -5 = o(15) r(18) -5 = m(13)
But since "wyndwz" = "windows" (intentional misspelling), "danlwd" = , "fyltr" = filter , "shkn" = shark ? That doesn't fit.
That gives "olywho"? No.
→ "atgom" — not a word. So not ROT-5.