The biggest problem with war crimes is it's the victors of war who get to decide who committed war crimes, and who didn't. It's mired in geopolitics and has very little to do with fair, rigorous and non-discriminating law.

Ethnic cleansing is a war crime. The UK is guilty of this where it comes to the Chagos Islands. Have the UK been charged with war crimes relating to this? Of course not, the USA has a military base on the islands. No international court to my knowledge has acknowledged the eviction of Chagos Islanders as ethnic cleansing, and therefore it's not legally a war crime, even though morally it probably is.

Sexual violence is an iffy subject, too. I am in no doubt there are lots of USA and UK soldiers who cracked under the pressure and committed atrocities, including sexual violence. I personally knew someone who beat a man to death with the butt of his gun, in front of his child, because the man "wouldn't shut the fuck up". This same guy was in a convoy that got hit by an IED, and he says he had to pick up body parts of his friends. This is just what he would talk about. Notice I said "knew", as in past tense. He killed himself because he couldn't live with his experiences. He was traumatised and consumed by immense guilt. He was broken. This is what happens when you send naive kids into war zones.

War crimes, as defined by Wikipedia, are happening all the time, from all sides, wherever war is happening.