KK preflop

I don't whether people on party at NL2 generally stack off with AA only because I don't play there.

However, I think that the 3bet OOP should definitely be larger (about 4 times the original raise).

And if people raise after a 4bet to 21bb, it is usually all-in. After your 5bet to 43bb, you are pretty much committed anyway because you have 40% of effective stacks in the middle. That means you need only about 30% equity to call. Unless you assume that villain has only AA or KK, it is always a call. And if you assume that he only has AA or KK, there is no point in 5betting anyway.

Now, the size of your 3b is too small. Maybe you have a reason for it - for example, you do not want to scare him, bla, bla, but you have a strong hand and you want him to continue strong too.

There is nothing wrong with stacking off with KK.

First of all, 3b PF should be bigger. Why do you use min 3b sizing? WTF?
Second, I mostly never fold KK preflop, only vs pretty narrow 5b range with a lot of hands vs villain sometimes I fold.

3bet bigger and after that your 5bet can be a shove. Pretty easy stack off here.

Thanks for the help. I will definitely be looking to make my 3 bets bigger in the future.