Terrible install! Just kidding
Looks really nice. A clear trap with a cleanout installed inside a galvanized drain pan would be better.
Here in my area insulation can't be crushed by straping and if it has been then a additional layer of insulation is required.
All primary drains above a ceiling in to be insulated. I would also have a tee and cap on the p trap for clean out.
The flex duct installation directions that come in the box of flex duct states that straping it to be no longer that every 5' and not to permit more than 1" of sag between straps. Also straping the flex duct on the outer sleeve crushes the insulation and can cause it to sweat and tape can come off then duct becomes loose.
Plastic drain pan these get brittle over years of hot attic temperatures. They also might want to install a float switch in the aux. drain pan.
Only thing I'd do is bring up the high return higer.. It seems to be in the middle??
Odd to see see both high/low return?