Crust: Preheat oven to 325°F (163°C). Mix crumbs, sugar, butter, and salt. Press into greased pan bottom and 1 inch up sides. Bake 10 minutes. Cool.
Filling: Beat cream cheese on medium 2 minutes until smooth. Add sugar, beat 1 minute. Add eggs one at a time on LOW speed — just until combined. Add sour cream, vanilla, lemon juice, and flour. Mix on low until just combined. One final fold with a spatula.
Wrap & fill: Wrap springform pan in two layers of heavy-duty foil. Pour filling over cooled crust. Smooth the top.
Water bath: Place wrapped pan in roasting pan. Pour hot water around it to 1-inch depth. Bake 55–65 minutes — edges set, center wobbles.
Cool: Oven off, door cracked 1 inch, leave 1 hour. Cool on rack 1 hour. Refrigerate 6+ hours, ideally overnight.
Topping: Cook blueberries, sugar, and lemon juice over medium heat 5 minutes. Add cornstarch dissolved in water. Cook 2–3 more minutes until glossy and thick. Cool completely. Spoon over chilled cheesecake before serving.