This is a respectable first grow. Coco is a bit harder to master than soil. I’d be very happy with what you accomplished. Autoflowers throw so many variables in the mix that you can’t account for.
I’d say maybe a bit over fertilized, or some salt build up causing tips like that. I’d maybe do real light feeds next 5 days and chop by the looks of things.
Try some photo genetics.. much easier to steer things in the right direction and have a predictable timeline.. and so many more other things
Also the defol mid flower was a BIT overkill IMO for an auto. Nice work tho truly on your first grow