Turns out it was a Caesar shift of 5 backward:
But if it’s an (A↔Z, B↔Y, etc.), let’s test first word “thmyl” → t(20) ↔ g(7), h(8) ↔ s(19), m(13) ↔ n(14), y(25) ↔ b(2), l(12) ↔ o(15) → "gsnbo" — no. thmyl ttbyq dyzny bls mhkr
→ shifting each letter back by 1 (or forward by 25) gives: "sglxk ssaxp c xymx akr l gjq" — doesn't make sense. Turns out it was a Caesar shift of