I’m not sure what the law is in the UK, but in the U.S. the embryos are the property of the parents, not the clinics.
If a million embryos/yr are destroyed in UK clinics, and the parents of those embryos are deciding to do that, then those parents are individually making the sinful decision to do so. It doesn’t mean IVF per se is sinful.
I would say U.S. fertility clinics are very respectful of embryos, fresh or frozen.