1 i don't like 4betting against a 6% 3b who plays otherwise loose pre (so they probably play bad post flop). you want to find yourself on rivers like this and be able to shove, but u can't do that if they only 3b 6%

2 id jam flop, or at least raise. i think your small 3b makes them give you less credit pre, so their 4b is wider and thus they aren't as nutted as it might seem on this flop. after making a cheesy 3b pre i definitely wouldn't play if this way unless there was some other reason i thought they might be very strong

3 id bet bigger on flop and not over bet turn. this way you can still shove river. but also there are lots of strategies you can take 99 here just be aware of balancing

4 don't hate it. the bluff price is good but you might get more respect if it was deeper