The four-cell route
Trace OPEN through 1 at row 4, column 5; 2 at row 5, column 5; 3 at row 5, column 4; 4 at row 5, column 3. Read those cells as O, P, E, N. The route begins with a downward move, then turns left and continues left for its final letter.
All four cells lie on the board’s edge. The turn comes after P, so the last two moves run in one direction rather than making another corner. Once this four-letter path is placed, four of the 23 open cells are assigned and 19 remain for the three longer paths.
Check the shape as well as the spelling: this path spans two rows and three columns, with its final three letters on the same row. Its single turn is at row 5, column 5. A trace with another turn may still collect familiar letters, but it does not follow this four-cell route.