Israel is a tiny country and in the event of war, Iran can easily devastate Israel by attacking its air force, civilian infrastructure and ports with ballistic missiles, cruise missiles and suicide drones.
1) Israel has 300 combat aircrafts: 600 ballistic missiles (2 missiles per target) backed by 600 cruise missiles and 3000 cheap suicide drones will devastate Israeli Air Force even if strike is only partially successful. If some aircrafts survive, they will not be able to enter Iranian airspace because of Iran's multilayered air defense network. Also distance between major cities of Iran and Israel is more than 1500km, which means most Israeli aircrafts don't have the range to reach these cities and even if they enter Iranian airspace they can make only small number of sorties against Iran because of huge distance.
2) Israel has 12 powerplants, 12 desalination plants and 12 other major infrastructure facilities: 5 missiles per each facility and you need 180 ballistic missiles to destroy these facilities and leave entire Israel without electricity, water and gas. Such strike can be backed by cruise missiles and drones.
3) Israel has 3 major Ports- Haifa, Ashdod and Eilat: Iran can impose a blockade of these ports by attacking all vessels that enter these ports from the Mediterranean Sea and the Straight of Tirana with Shahed-136 drones with electro-optical seeker, launched from Northern Iraq and Western Syria. Eventually you will impose a blockade of Israeli ports and leave Israel without trade.
But Israel can use nuclear weapons against Iran. But it is possible that Iran already posseses few nuclear warheads obtained from the old Soviet nuclear arsenal. - Now you will say this is a conspiracy theory, but reports about Iran purchasing several nuclear warheads from the former Soviet Union came from credible sources like BND's Paul Munstermann. Russian General Yuri Baluevsky also said in early 2000s that Iran posseses tactical nuclear weapons.
Also US can enter the war, but Americans are pragmatic people who never enter irrational, counterproductive wars that can do a lot of damage to their country and their people. US knows that if they enter the war, Iran will close the Straight of Hormuz (20% of world's oil) and Straight of Bab-el-Mandeb (12% of world's trade) and this will have devastating consequences for the world in general and for US in particular. Also, In the early days of the conflict in Gaza, IRGC said that they have the capability to close maritime traffic in the Mediterranean Sea, Suez Canal, Red Sea and even the Straight of Gibraltar. So Americans will stay away from Israel-Iran war because they don't want global depression.