The US would block the necessary UN resolution for this at the security council, because it’s against one of their closest Allies. Since the late '60s and in earnest the early '70s, there has been a strong relationship between America and Israel. Shared values, shared enemies, shared economic interests. This support is bipartisan, with both Democrats and Republicans overwhelmingly recognizing the strategic importance of Israel to the US.

This kind of resolution would also set a dangerous and illogical precedent, essentially signaling that it’s illegal for countries to use their armed forces what they are ideally used for, destroying forces hostile to their home country that struck first or pose a serious threat of striking first, which in turn signals to terrorist groups like Hamas that they can attack and that whoever retaliates must fear UN intervention.

Then there’s the whole business that absolutely nobody would want their troops to be fighting Hamas directly or play peace keeper in this hideous powder keg (remember the UN doesn’t have its own army - blue helmets are just soldiers from member states), because this would potentially invite Hamas and other Islamist extremists from using this as an excuse for terrorist attacks against them. This isn’t unfounded: See several Hamas plots that have been uncovered recently, like in Denmark and Brazil. Hamas is not just a threat to Israel and they are not acting alone, but have relationships with other Islamofascist organizations.

Absolutely nobody would want to risk an armed clash against Israel either (because I don’t think they would just accept an international coalition, even with UN mandate, endangering their sovereignty): It has both formidable conventional capabilities and is nuclear armed, including with nuclear-armed submarines and ICBMs. This strong deterrent - only about a third of their armed forces are engaged in Gaza right now, the rest are guarding their borders - essentially gives them immunity against direct attacks and other hostile actions from state actors (everyone who tried in the past, when Israel was significantly less powerful, failed, even when they outnumbered and outgunned Israel, even when they had a technological edge, very much unlike now), which is why Iran in particular has to use proxies with a thin veneer of “plausible” deniability to engage this arch enemy of theirs or else risk anything from a painful retaliation to total annihilation.

There is also the economic factor: Israel is the Taiwan of the Middle East, with a high-tech economy that is extremely important to the world. Items like 10nm computer chips are vital to the global economy. An embargo against the small nation could have potentially devastating effects. Embargoes that only target arms don’t make much sense either and would be toothless: Israel is a major producer of high-tech weaponry and several armed forces in the world partially depend on supplies and technology from them. They can produce almost everything locally, only using e.g. American-made bombs and interceptor missiles, because it’s faster, cheaper (or free). The times when they had to smuggle in hunting rifles and scrapped tanks due to an American embargo against them (which existed until the Kennedy administration) are long over.

Israel is one of very few countries that has the ability to develop nearly every weapons system known to man and produce most of them locally, including small arms, armored vehicles (including tanks), drones of all kinds that make those used in the Ukraine war look like toys, multirole fighter jets (they have mothballed programs in the past in favor of buying American aircraft - but they are capable of reverting this decision), all sorts of defensive systems they invented, like Iron Dome and Trophy, naval vessels (co-designed or entirely in Israel and built elsewhere, but they could likely build them locally, at a great expense) and of course their dual-use space program, by which I mean that their ability to launch multistage rockets gives them both the ability to send satellites into orbit and hit any point on the planet with ICBMs. I don’t remember where I read this, but they essentially have factories ready to go that can be activated within days if American and other currently existing international support was ever suddenly cut off and/or they needed a large amount of arms and ammunition very quickly, e.g. in case of a multi-front war. The reason for this is that in the past, vital arms supplies to them have been cut, e.g. when the British refused deliveries of tanks, which led to Israel developing and producing their own.

The gist of it is that they have friends in high places, are - even without those - simply too powerful on their own and that nobody else wants to touch Hamas with a ten-foot pole.

I hope this clears up why your idea is completely unrealistic. If you have any further questions, feel free to ask.