"No matter what Hamas did, it does not justify the incredible use of lethal force without distinction and without proportionality as far as the Palestinian population is concerned in Gaza,” says Sven Kühn von Burgsdorff, recently retired European Union ambassador to Palestine, adding that “Israel must adhere to international law and protect civilians.”
Hamas is trying to create a situation where they can strike Israel and then claim that Israel cannot strike back, because Hamas is aiming to use human shields.
The rules of war don’t give Hamas that ability. That is, they do not say “Israel is obliged to not fight in cities, even if Hamas chooses to make that their battleground”.
The major source of protection for civilians in war is the Fourth Geneva Convention, and it explicitly states that this cannot be done:
https://www.ohchr.org/en/instruments-mechanisms/instruments/geneva-convention-relative-protection-civilian-persons-time-war
There are restrictions that aim at limiting the impact on civilians where this can reasonably be avoided in the Geneva Conventions. If Israel were to cut off civilians from retreating from a city, that would be problematic, but they have not done that; on the contrary, they have warned that there will be military operations occurring and that people should leave the area.
If civilians are trying to leave and provision might be made for evacuation without prejudicing Israel’s military operations, then one might make a reasonable argument that Israel is obliged to make that provision. But Hamas doesn’t get to claim that they cannot be attacked.