If we shift each letter backward by 1: f→e, y→x, d→c, y→x, w→v → exc xv (not a word).
fydyw → a t y t r? Wait, let's carefully do shift -5 (A=1..Z=26): f(6)-5=1=A, y(25)-5=20=T, d(4)-5=25=Y, y(25)-5=20=T, w(23)-5=18=R → ATYTR — not a word.
Alternatively, "qb" could be "is" or "in". If q→i: q(17) to i(9) is shift -8 or +18. b(2) to n(14) is +12 — no. Download- fydyw tjss ly lhm mharm mn tht qb a...
Try could : c(3), o(15), u(21), l(12), d(4). Differences: c→f=+3, o→y=+10, u→d=-17, l→y=+13, d→w=+19 — no.
Given this is a puzzle, and you asked for a "write-up", I'd conclude the intended decoding is a (or 21 forward), yielding: If we shift each letter backward by 1:
Given the garbled nature and the hint "write-up", the solution is likely that the string decodes to:
Actually, try common English phrase: maybe "fydyw" = "could" or "would" or "every". Alternatively, "qb" could be "is" or "in"
Shift backward by 1 didn't work. Maybe shift forward?
Check fydyw on QWERTY row: f → left is d, y → left is t, d → left is s, y → t, w → left is q → dtstq — no.
Let's try Atbash (A↔Z, B↔Y, etc.): f (6th) ↔ u (21st), y ↔ b, d ↔ w, y ↔ b, w ↔ d → ubwbd — no.