Cites for the groups alleging that Israeli airstrikes have been indiscriminate are in the Wikipedia article and include UN special rapporteurs, the United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA), The Greek Orthodox Patriarchate of Jerusalem, the United Nation Human Rights Office, and Amnesty International. I would imagine others have also made the accusation.
Investigations by appropriate authorities would need to be undertaken to substantiate or refute the allegations.
Over a hundred people were reported killed and a market and residential complex destroyed. This raises the question of proportionality in that the incidental civilian loss or damages must be proportionate with the military advantages. If this proportionality requirement is not followed, humanitarian law considers the attack to be indiscriminate. I’m not a war crimes lawyer, so I’m not able to assess the particulars of this case. The United Nation Human Rights Office stated, “We have serious concerns that these are disproportionate attacks that could amount to war crimes.”
Israel’s president Isaac Herzog accused the residents of Gaza of collective responsibility for the war. The Wikipedia article cites various groups and individuals describing the situation as collective punishment, including Doctors Without Borders, Oxfam, the EU’s chief diplomat Josep Borrell, the UN Secretary-General Antonio Guterres, and Human Rights Watch.
I’m not a lawyer, but it seems incredibly war-crimey to me to deprive over 2 million innocent civilians of food, water, supplies and so on in order to try and deprive a targeted 40,000 armed individuals of the same.