i am not look down your country but your country is safe and rather money to development then buy advanced fighthers.
I search wiki and found you only have 8 MIG-29 and 47 J-7.
I think your country dont need F-35/SU-57/J20/TF-X/KF-21 in the neraly future
Bangladesh is very exposed.
They have a clearly hostile and unstable Myanmar as a neighbor. Their land is almost surrounded by India and Bangladesh is trying to balance Indian, Chinese and American influence.
They need a strong Air Force, Army and Navy to maintain full independence and avoid bullying.
Luckily their economy is strong and they are more prosperous that their neighbors.