Qualcomm withheld the kickbacks partly because Apple violated their contract by giving false evidence. (Apple should not complain... their contracts with their suppliers are even worse.)
E.g. Apple told the Korean FTC that they were unable to buy modems from other makers. Poor, poor Apple. Then about six weeks later, the new iPhones came out using Intel modems. A more blatant lie would be hard to find.
We all do. Qualcomm invented the 3G that everyone uses/used. And they're a huge part of 4G, 5G and beyond.
Without Qualcomm spending billions of dollars a year on R&D, we wouldn't have all that. Certainly Apple isn't gonna do it.
Except that's exactly how most every member of ETSI charges. Nokia, Motorola, Ericsson, Sony, LG, you name it... they all charge that way so that higher profit phones subsidize the ability for companies to sell tiny profit phones.
And without those billions of tiny profit phones, there would have been NO WORLDWIDE NETWORK for phones like Apple's to use. Apple hates it because they refuse to sell a low profit phone.
Charging by percentage is a totally legal and common way of licensing IP. Heck, even Apple licensed their own IP that way. So any argument otherwise is just nonsense. It's all about money, not right or wrong as Apple's PR would like us to think. Tim Cook sees sales slipping and he needs more profit any way he can get it.