So here it is:
Actually — I notice "thmyl" if each letter is shifted one forward in alphabet: t→u , h→i , m→n , y→z , l→m → uinzm — nonsense. thmyl fysbwk layt andrwyd 2.3.6
Test simpler: Could thmyl be th + myl = the + my + l ? th = the? No. So here it is: Actually — I notice
Given the last part "andrwyd 2.3.6" , that looks like a version number or coordinates. "andrwyd" could be "and ruwyd" or "and rwyd" ? rwyd → rwyd might be "rwyd" as in "rywd" ? Could be Welsh: "and rwyd" (and net?) but "thmyl" doesn't fit Welsh easily. thmyl fysbwk layt andrwyd 2.3.6
On the back, handwritten: "Thmyl fysbwk layt" — code for: "They will forget you last."