It can be summed up as he doesnt like that Peter in the MCU is always looking for approval from people (Stark in particular) as opposed to being confident, cocky and self assuring when he puts on the mask, which is how he acts when he's Spider-Man, where as movie Spidey got chastised by Stark, original Spidey would've gotten pissed and Webbed Stark up and tended to butt heads with people who rubbed him the wrong way (Daredevil, the Fantastic Four, etc).
After you said this I listened to his podcast from today about this, and yeah that's a solid explanation of some of what I dislike about him.
It really sounds like Pat has had a huge turnaround from liking him in Civil War to being solid with him in Homecoming to finally disliking him in Far From Home. My turn to dislike was way faster personally (liked CW; thought SMH was bad; think SMFFH looks awful) but it's pretty interesting that someone else who loves Spidey has turned on him that much.
I was thinking about it earlier today, and while I've had people tell me that it must be my dislike of the high school setting, it's not even the setting that grates on me. I
do prefer his ESU and post-grad storylines, but I
loved Ultimate Spidey and that's a distinctly high school Peter. And of course Miles is still in secondary education, and he's great too.
Eh whatever, it's not for me I guess, and that's fine. Not worth belaboring the point too much.