EDIT: the reason it cooks food is the intensity of the field strength (1 kilowatt per cubic ft, or ~27,000 watts per cubic meter) in a microwave oven. 5G signals are tens of microwatts (millionths of a watt) per cubic meter. That's a difference of a factor of 10's of billions.
power from your phone: 0.2 watt in case of LTE.
reveived power from a basestation: around -40 to -120 dbm.
You are 100% sure that will have absolutely no impact on insects or birds in close proximity to it?
But even if it would be 500W, no haven't heared of it. Which does not mean that it could happen. But then again the question was not a) insects or birds or b) close proximity (which is what, close then 1m?)
Not really. 2.4GHz was chosen because it allowed to built microwave ovens at that particular size and because nobody cares about the 2.4GHz range. You can build 900 MHz ovens too, there are some, mainly for industrial usage.
The wavelength of microwave ovens is even longer, at 6.66cm. And yet that's the rotational resonant frequency of water. Weird, huh? By the way, you can confirm this with a single slice of cheese with the turnplate removed and then calculate the speed of light from the burn marks on that cheese being 3.33cm apart :)
The only question is whether that reaction at any given frequency has any impact on the larger system those molecules are part of.
The answer is scientists aren't sure because they haven't had a chance to experiment much, and you and I are sure as shit not qualified to comment on it.
I'm not going to don a tinfoil hat over 5g rollouts, but this cavalier attitude of just expecting everything to be fine without any meaningful testing is just as bad if not worse than the conspiracy theories.