Here is a look at Trubisky's deep ball numbers on the year (15+ air yards). Listed in order of Air Yds from most to least. Should be noted that included in here is the Miller dropped TD vs NYG, so if your into adjustments you can add a TD at 16 AY.
Mitch is actually pretty good in the 15-20 air yard range. This is where he tends to live, as far as downfield throws go. Anything beyond 20 air yards starts to get rough though.
Which still seems odd to me. He hit Gabriel 30+ air yds downfield in 2018 multiple times. In 2018 in general, he had many more deep attempts, and much more success than he has seen in 2019 & especially in 2020.