Place a piece of white paper under your plant, above the medium. Cut a slot for the stalk. Gently but firmly shake the plant for a about 15 seconds. CAREFULLY remove paper and shine a light source through it...if there are critters, you will see.
FF
Definitely not mildew. The somewhat uniform spots indicate missing nutrients - possibly not the NPK but rather micro nutes like trace minerals. Have you been adding those? Eg chromium or manganese?
Also I wouldn’t jump into defoliation - the plant in flower light mode will start stretching fast and it needs all the leaves that stored nitrogen it can get