Self defense is not a war crime. Overwhelming violence against an active aggressor is not immoral. You can’t be lukewarm about war; it is an all-or-nothing proposition - you either win or die. Israel will never win the war of public opinion, so they may as well inflict as much damage to the enemy as is required to put a final end to enemy attacks. Showing restraint has not stopped attacks against Israel since its inception. It is no consolation to be morally superior if you are dead.
and...... every live person in Gaza is a combatant
If Israel targeted Palestinian civilians in order to kill them and in order to get them to leave the country and force a mass migration of the population (which is exactly what the enemies of Israel claim it does) - then that would be a war crime.
If Israel targets Hamas operatives and Hamas buildings and war material, and avoid hitting Palestinian civilians (which is what Israel says it does and “does”) - then that is not a war crime.
The second of the two paragraphs is what Israel actually does and which the ENEMIES OF ISRAEL deny that they do. Also those who “feign support” for Israel also are the ones who urge Israel to commit war crimes (and Israel doesn’t listen to those “faux-supporters”).