Well, the atrocities against the Native Americans are indeed where the line becomes blurry. European settlers wiped most of the native population and took their lands, but it's still up for debate which parts, if any, of that can be called a genocide. It's also questionable whether cultural (e.g. what the Chinese are doing in Xinjiang or the Americans and Australians attempted with forced adoptions) count at all. There's not even a consensus the trail of tears counts. That's how high the bar is. You can murder countless, but as long as you "only" want to steal their land or kill them for any other reason it's not a genocide. For genocide wiping the people in qusetion has to be the point, not just means to an end.

Hence clear cut genocides are indeed quite rare. The Shoa was one, so were the Armenian genocide and the Rwandan genocide, but wars rarely count, regardless how destructive they are.

Therefore considering what is happening in Gaza a genocide is - for now - a huge stretch. That's why the ICJ didn't even ask Israel to stop thier military campaign. The court merely affirmed it shouldn't actually start a genocide.

All that said, what Israel doing clearly not being a genocide does not mean it's entirely legal. The threshold for war crimes is a log lower.