KF-21 doesnt have internal weapon bay for stealth flight capability
KAAN is a 5th gen Fighter Jet
-- with stealth design , advanced magnetic coating and RAM panel layer
-- with internal weapon bay
-- with sensor fusion ... ( 4 AESA Radars , IRST , EOTS , HMDS )
The F-135 engine runs at 1980 degrees, meaning a very high heat signature.
The F35 has structural cooling to reduce this signature. However, with this cooling, the heat signature still cannot decrease to the level of the F110 Engine
The zigzag nozzle in the F-35 increases the 360 degree stealth feature
but it does not necessarily have the 360 degree stealth feature against F-35 , SU-57 and J-20 in head to head engagement
While KAAN is going to the enemy lines, it will meet the radar from the front.
and KAAN has 5th gen capability from the front line ( head to head against the F-35 , J-20 and SU-57 )
We won't have to worry about F110 Engine giving more views from behind in head to head engagement
GE-F110 engine is a good engine but only 29.000 lbf
So,, if J-20 and SU-57 5th gen Fighters then KAAN is also a 5th gen Fighter
btw 35.000 lbf indigenous Engine will give the 360 degree stealth feature to KAAN