The US and even Israeli governments consider these numbers as accurate. The Health Ministry provides the social ID numbers of every death so the deaths would be impossible to fake.
Do you have a link to the officially published name, sex, age, ID, of all the victims so far, by date, in the conflict?
When large buildings are demolished by bombs and can't be excavated because of active violence what's the process for figuring out who potentially was or wasn't in that building? with all the refugees moving around the chaos how do you know if someone who used to live there is dead or sheltering somewhere else out of contact?
Hamas reports everyone as civilians (or doesn't make a distinction).
EDIT: While trying to find this from another source I found this: https://news.sky.com/story/israel-hamas-war-health-system-co...
"Of the 21,703 identified fatalities whose details have been shared by the Hamas-run health ministry, 13,207 were women, children or elderly (61%)."
"Until recently, however, the ministry had been reporting a figure of 72%."
"Mr al Wahaidi told Sky News that this was a "media estimate". He was not able to explain the basis for this estimate or who had produced it."
"Since speaking to Sky News, he has stopped using this figure in his reports for the health ministry. It continues to be used by the government media office, a separate branch of Gaza's government."
...
"media estimate". Another by the way is that I think we should assume that given the significant bombing campaigns are more or less over the more recent casualties likely include less randomness and more targeted. I would guess that the ratio of women/children/elderly is much lower in more recent stages of the war.
Not included are a large number of missing people, and all the people who die of secondary causes like maltutrition, disease outbreaks, and poor access to proper medical care.
Nobody really knows what the real casualty figures are, but I'm inclined to take the Gaza Health Ministry's numbers seriously -- as do Israel and the US, as you already mentioned.