Ethnic cleansing is a horrific crime. It usually involves marching entire populations into a desert, getting them to dig their own graves, and shooting them. That happened to the Yazidis. It happened to the Armenians during the creation of Turkey.
You minimise those crimes when you appropriate the word for some hysterically imagined future, based on Trump saying he'd like to own Gaza.
I'm quite sure that whatever happens in Gaza, some people will keep shouting 'ethnic cleansing', and will find some way to twist the definition to include it. It's wrong, and you shouldn't.