2 diamond shaped things look like antennas, the others seems like APU exhaust/intake.
Because you would have 2 different spill panels, respective to S duct locations?
He is a Korean ultranationalist (I suppose) whom also supports PKK/YPG and to add all on top of that, HE CLAIMS THAT J-20 IS BAD AND KF-21 IS MORE STEALTH THAN J-20.
Please don't take this account seriously, he is an "expert" by no means
As you can see, most of the stuff is done by body thickness and engine cooling intakes (which is not related to engine)
TF-X with F110 will definitely be better than F-16 or some 4.5 gens but won't be good as F-22/F-35
Well it is also related to intakes, F-15EX with same engines can go lot faster than 1.8mach, but has a variable ramp, F-22 also has it but it affects RCS iirc