Brown spot on leaves: Nutrient/ph issue or fungal disease? or both?

If you noticed a verry high EC this might just be the after math from it. It does look like some phosphorus issue to me based on the small leaves and how the damage progressed but normally that starts on the lower leaves first not the upper. So before trying to treat anything, Get your EC in line and PH then see if it is progressing, If it is not, problem solved no need for anything. If it is progressing still time to look into other options. This link is nice for a descent leaf chart. https://420life.com/wp-content/uploads/2021/10/Marijuana-Leaf-Deficiency-Chart-scaled.jpg Again fix EC and PH first before trying anything else. Plants are looking nice and healthy otherwise. Good Luck!

Lacking Phosphorous. The question is, why? Insufficient quantities? Excessive salts around the roots causing lock out? Out of Range pH? You might have too much phosphate in the soil. Are you growing in Coco? Is the coco drying out frequently?