Is IVF with Sperm donation or Egg donation prohibited in islam?

Earlier I read in many articles that IVF is haraam since it is an unnatural way. But now its considered OK but only with the fusion of sperm-egg of a married couple. I have a doubt that why is pregnancy considered haraam using egg donation or sperm donation, and considered to be zinaa. As far as I know (not very sure) zinaa of the body is to GET PHYSICAL with someone you are not married to (adultery). So in egg/sperm donation, people are not getting physical, so how could we term it as zinaa ? Also, if a lady isn't getting pregnant naturally, and to avoid her divorce would it be wrong to go for egg/sperm donation ? Because no matter how loving you are, an adopted child would always be an adopted child, as he deserves to know his lineage. Once he knows his actual parents, its very likely that the love won't be the same. Also, isn't getting a child with egg/sperm donation better than getting a divorce (divorce is a thing that Allah s.w.t hates most). ?