IMO, BD doesn't need fighters against Myanmar. Best thing against them would be layered SAMs which I have a post about, and GLCMs.
BD could use 100s of GLCM against Myanmar's bases in within strategic range of BD that could be used against BD. Layered SAMs could shoot down stragglers that escaped barrage. BD shouldn't get Chinese GLCM if possible, and go for a third party that isn't Russian so that they can be used against both India, and Myanmar.
I think BD needs to introduce in numbers 4+ gen aircraft as well as master the capabilities it brings.
That process will take a while.
Also, specifically against Myanmar, I don't see a full scale war.
However, it may be a border skirmish which escalates to some degree.
For that scenario I think a strong and capable BAF provides a deterence factor even before hostilities break out.
Lets be real, Bangladesh is not really an aggressive country.
The society is actually very docile.
But what it needs to guard against is a nasty neighbor to the East.
And a frenemy which surrounds it on three sides.
The advantage BD has is its political capital in the West.
Use it to obtain modern systems which Myanmar may not have access to.
That includes of course fighter aircraft and the relevant munitions.
Enter F-16, Gripen or Typhoon.